I've used every type of phone grip that exists but none of them have been comfy, stable, washable, non obstructive, AND compatible with car mounts. I got an idea to make my own though. just nubs added to an already existing stl for a case.

hair ties hook between nubs to form repositionable grips. if the hair ties wear out or get yucky they can be easily replaced. also if I need a hair tie, one will be on hand at all times lol

nubs are 100 mm apart (in the positions where I intended hair ties to go) which stretches my hair ties enough that they will stay put but not enough that makes them hurt to get my fingers behind them. that top nub will be removed btw. there's no real point in putting one up there.