I’m from Phoenix, but more recently lived in Tucson for several years. With that caveat, here’s my recommendation:
Scottsdale is the most obvious answer for where to stay. It sounds like your partner enjoys the city life, so I would avoid North Scottsdale as it can be a bit of a snooze nightlife wise. Anywhere in central Scottsdale (near-ish to Old Town, but probably not in Old Town) should be fine. Downtown Phoenix (and even Tempe to an extent) has more cultural offerings but entails more traffic-heavy city miles to access some of the main rides in the area, so weigh that if you’re considering staying in a more “city” environment. The one exception to this is South Mountain, which is located in South Phoenix, and fairly easily accessed from downtown.
Depending on where you’re coming from, the riding isn’t spectacular (I might be biased here), but there are some good desert loops to be had, most of which are located near Scottsdale. If you do wind up staying in central Scottsdale, check out Bike Haus for group rides or route beta. A trip to Tucson to climb Mt. Lemmon is well worth it if you have access to a car.