Travel Tip, Here is a simple way to lose a smartphone on Planes, Trains, Buses, and Taxis
I had a similar problem.
I now only wear a shirt with a pocket. When I'm driving wearing a seat belt I put my phone from my from my pants pocket to my shirt pocket. I made up a small alligator clip with a plastic probe to to fit into my cell phone ear plug connector to pin to my shirt pocket to keep it from falling out if I bend over.