I wanted to mount my CB mic but without drilling.
This bracket attaches to the passenger grab bar (note this is for a RHD jeep but you can reverse for LHD)
I printed a clip for the CB and 'superglued' it on but you could incorporate one into the design.
You could also add a mounting plate for a specific phone.
It's not too fancy (I just quickly designd it in 3d Builder) but it works.
Update... I have added a more rounded version with the CB clip integrated.