I have an iFitness belt that I use to carry my phone when I run - www.ifitnessinc.com/.. I have a neoprene double pouch - one pouch for my iPhone and one for my sport beans. I also have the hydration bottle add-ons so I always have water as well.
Can't you do without your phone for the length of a run; or does it have an app to check your cardio?
I know a lot of people use them to listen to music while they run. I take mine for security purposes - in case I fall and get hurt or the weather turns nasty and I need to be picked up. I run trails that often take me anywhere from 6-10+ miles away from my car.