Spring Phone Cradle - Revision 3

I'm in the process of creating a bespoke centre pod in my car, to hold my mobile phone in landscape mode when I use GPS. I've almost finished the main pod assembly (which will be another "Thing" in due course. UPDATE: See thing 3125678), but I had to devise a way to actually hold my phone securely whilst the vehicle was on the move.

But how to get that essential grip? I know elastic bands are popular, but a car's interior environment isn't friendly to rubber bands over any sort of time. They