Picture of Smartphone holder for bicycle
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. 
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Step 1: How to make a short loop.

Picture of How to make a short loop.
Then fix the rest of  the  belt loop by rubber peace of camera

Step 2: & On backpack

Picture of & On backpack
can be used the same loop. Then phone is in very good place for  call answering and talking in hands free mode.