Here's a solution that I am using:

You may find that if your flip phone has a hole for a thin nylon cord, you may be able to loop a small Victorinox replacement split ring through it and attach a para cord lanyard. The large Vic split rings are too big, at least for my phone. I tuck the red wooden ball up between my pants and belt, and the phone dangles. If I get a call, a quick tug loosens it. I can hang the phone in a pocket if I'm in the woods. It does not fall out.