Yes! That! I was dropped on a group ride (people thought I was taking a piss) and yet had a technical issue and ended up calling my wife and dealing with her yelling at me for being over 50 miles away and in the hinterland of an agrarian area that was literally ‘out there’, MILES from civilization. I was pissed that the group just abandoned me, but without a cellphone, it would have been a hell of a walk back to my car. But I also had to rely on others once when I flatted TWICE, and went through the tubes I had on me. It goes both ways I guess, I’ve donated a few tubes in my career, but I would be a little miffed if someone didn’t carry even one on a ride. You have to be prepared, but you don’t have to carry a dozen. (For the road bike, I do tend to carry three lightweight tubes if I’m riding long, JIC)
I bring a phone so I don’t have to rely on the kindness of strangers. I bring a multitool, a plug kit, and a tube for the same reason.
I don’t bring my phone on most rides. My reason is I don’t want to get distracted by it at stops and stare at the screen.
I do wear a cellular Apple Watch if I need it in an emergency - it automatically suggested to call emergency services when I came off the bike a couple of times.
So it’s not about the weight. I carry a pump, tool and plugs (which by the way I will always offer to a rider who chooses not to carry those). I also carry a Ricoh GR sometimes if I want to take pics.
Basically it’s about reducing iPhone distractions, which is why I own the watch in the first place.
If Garmin put a SIM card option in some of their devices again at least as optional it would be ideal for me - I almost always have an Edge out front already.
My Apple Watch has full phone service and works in place of my phone if I leave it in the car. I can also stream all music through my watch.
That being said, I don’t like wearing it during my rides and phone is more convenient in case of pics or texts.
All that aside, I’m pretty ocd about not stopping my rides so never text and rarely take pics most places I ride. It’s still easy to carry the phone in my top tube bag.
In the future, I may start leaving phone with my wife in races and just carrying my watch in a top tube bag for emergencies and music streaming (I’d also consider just removing the band). My wife can also track me on my watch with find my friends.
The Apple Watch monthly plan for connectivity is only around $15/mo.
Which is fair and is essentially the same as carrying your phone.
Just put it in a saddle bag or top tube bag and don’t look at it. Only pull it out if you need it.
Reasons to: emergencies, updating loved ones on progress, being able to recieve word of others’ emergencies, pictures/videos (strava!), maps, checking if x business (e.g. bike shop, cafe, etc.) is still open.
Reasons to not: … weight? Ensuring it will not get wet or damaged.
Pros outweigh cons.
The reasons not to carry are hard to come by IMO.
My phone is always set to silent and my Garmin only alerts for messages so there are minimal distractions or downsides. The upside of paying for cake, getting a rescue and making sure if I go down Dad/partner know where to scrape me up from.
Usually on a group ride you’ll be on your own riding to the start and a courtesy call/Text/ WhatsApp can help when you are running late etc. During the ride sometimes things happen and you end up on your own too and sometimes a similar a courtesy call/Text/ WhatsApp is needed. Even if you are not on your own you can be the only person in the group with signal too. At the end of a ride you’re on your own too until you get home usually. Not usually a thing for me (I live alone) but a quick message home can be important too. I hope to never need it, but for emergences against a few grams, I would rather my phone was there.
Weight.
Only ride I don’t bring it is when I go for a PR on my local climb.
Thanks for all the responses.
I guess growing up riding before the mobile phone, real helmets etc I didn’t see too much of a need for my phone. Not really phone guy, but I have destroyed 2 in the past 5 years. Wife loves it cause she gets the new one and I get her older one.
I’m not expecting anyone to bail me out either. I had to walk about 11 miles when I trashed a derailleur. Coasting down hill was good. Hike a bike up them was not. Don’t usually carry a spare one unless I was doing something like the Great Divide. It was a good walk. Saw more than I would have riding it.
As a cyclist I don’t mind helping others in need. I think most of us are that way. Once I rode 18 miles back to my truck because one of the group taco-ed a wheel. Lucky I could get my truck to him.
Maybe all your responses will convince me to start carrying it again
One again thanks.
I left my 300g phone/case at the base of a 1000m climb when I was going after the segment crown, among some other climbs where I didn’t want the weight. Other than races, I basically always have my phone.
I’ve been guilty of unloading all “unnecessary” weight for a segment or two myself. 
Same… then I’ve also been guilty of riding home, proud of my PR, before realizing my bottles and saddle bag are still on the side of the road somewhere 
To be fair, I have thought about getting a second/old phone, which would just have some basic apps, for rides where the risk of losing or breaking it is relatively high. I haven’t done it, because the technological advances of new phones make this a bit difficult. For example, 4G replacing 3G, with 3G signal getting worse. Or the ability to update mapping tools etc. And also because the picture quality is just better on a new phone… (I’m not rich enough to afford two “good” phones).
Just wanted to add, in addition to everything mentioned, with Apples new satellite capability it is even more indispensable. It was only for emergencies, but now is also for any messaging.
Several mountain bike trails I ride don’t have cell coverage, but also a number of gravel (and some paved) routes and races I do have spotty or non-existent cell coverage. So to be able to message in case of emergency is huge, but even to be able to message home when running late or something non-emergency comes up.
Another good reason to have a phone is this situation I’ve been apart of a few times - someone goes down hard in a group ride. While we all are waiting for the ambulance, phones start coming out of pockets to let those at home know the caller will be late and to make sure loved ones don’t hear about the crash first on social media and worry (the last part eventual resulted in a well observed moritorium on any crash posts until well after everyone is home).
I wasn’t there but a few years ago there was a horrific accident on a major charity ride in the area that resulted in two deaths and some very severe injuries. It was bad enough it was on the news fairly quickly. Every single person on that ride even if miles from the accident was glad they had a phone so they could check in.
My wife knew exactly where the ambulance was picking me up twice. Without the phone she would not know until called by someone. In one case that would have been 3hrs as that’s when I woke up in shock trauma. I can stand to lose more weight than the phone is.
I don’t normally carry my phone when I’m riding with my GF, because she always carries hers (two teenage boys and now grandkids on the way). But it was fun when I recently dislocated my shoulder on a jump behind her, and had to just sit and wait for her to notice and come back to find me sitting there 
Had her pull my arm to pop it back in and finish the ride.
Any other time I carry it though, since I have crash detection and mostly ride solo. I carry my inReach when off grid. But other than making sure I stay disconnected when riding with the GF, I see no reason not to carry it. But I’m also an introvert and talk to very few people, so my phone never buzzes unless it is my mom, or a handful of friends.
I dont carry my main phone due its size. It wont fit in a tool bottle (which already has other stuff in anyway), i dont have a saddle bag etc and hate stuff in my back pockets.
Instead i have a burner phone with essential contacts on incase i need to make an emergency call. Its tiny, weighs nothing, battery lasts months at a time and fits in the tool bottle with the rest.
Putting a lot of faith in humanity there. And it doesn’t match up with my experience.
I always carry my phone. Because one, I’m usually riding by myself. And even if you’re in a group, don’t want to be known as “that guy” who is unprepared? Do you not carry a saddle bag because somebody else on your group ride will have supplies? Second, I ride out in the middle of nowhere. So who knows if even a car will pass let alone one that will stop and help. If I’m riding trails it could be hours before another person passes.
Why take those risks when a phone is like 200g? I would choose a phone over a saddle bag with spares any day.