Doesn't it seem like stores charge far too much for simple items like mobile phone cases? Try making your own No-Sew Phone Armband and you'll end up spending a very small fraction of the price and it will only take a few minutes of your time.
Marta from the 2nd Funniest Thing has provided online instructions for this DIY mp3 player cuff. It just requires a plastic placemat in your choice color, two hair elastics, some glue and a pair of scissors. You might find a ruler and a pencil useful as well.
Place your iPhone in the center of the place mat and trace a cross shape around it. These help you to form the pocket and the straps for the No-Sew Phone Armband, which can be connected through the stretchy loops.