I don't know about iPhone, but Android has navigation gestures where you sweep from edge for back, from bottm for home and few more. I started to get thumb pain from light of small phone (S10e), and pain went away after switching to these gestures. Yes, these gestures have slight issues in some cases but you can't argue with RSI. Took a day or two to get used to. I assume pain came from scretching thumb too much for reaching controls on the bottom. So give it a chance if your phone supports something like that.