Just make a belt loop like this, to fix a sporting phone belt-holder on the bicycle. Put a small spongle in betveen. For better fix and amortization.
Step 1: How to make a short loop.
Then fix the rest of the belt loop by rubber peace of camera
Step 2: & On backpack
can be used the same loop. Then phone is in very good place for call answering and talking in hands free mode.