Phone accelerometers don't have enough range and sampling frequency to even begin with. Raw, on some rare phones you can sample 800 Hz (enough-ish), but on most 100 Hz max, Web API is capped at 60 Hz, this is all way too low for any quaternion math. They also have much higher noise density which is the silent killer of all kinds of IMU navigation.

I also wouldn't trust a strap to drop a loaded bar from snatch :D https://youtu.be/nrgnH9fTfGo?si=6LLeu3y02iFrwfis&t=65