Using a Samsung S4 with a non-official ROM to get a version of Android TR supports. (My S4 never got an official Android 5.x update.) In my experience, ANT+ seems to work more reliably and consistently than BT (even compared to a newer BT-only phone). Same proved true on an i7-7700HQ machine with an ANT+ dongle and BT–ANT+ seemed to be more reliable and consistent.
If the S4 ever dies (replaceable battery ) or TR ever requires a later version of Android that I can get for it, I’ll find another, old ANT+ supporting phone (likely Samsung since no one else supports it on phones) to make my trainer phone. (Though I see Lineage OS supposedly has an Android 10.x ROM available for S4, so…)
Or maybe by then I’ll be able to push inside workouts to my head unit and run the workout from that while TR listens on BT and records the workout and aligns it to the graph based on the head unit’s commands to the trainer. (Yes, that’s several feature requests in one. )