From Fehr Trade:
This armband has a pocket on one side with a simple fold-over flap for keeping things like a phone, keys, travelcard, etc tight against your arm while you run. There are no closures – the band just slips over your arm and the stretchiness of the fabric holds it in place.
Beginner sewing skills are required for this pattern - You should know the basics of sewing but may not have sewn with knits before.
The armband pattern requires 4-way stretch jersey fabric with good recovery - it is drafted to fit an iPhone 5 (if you need a taller or shorter pocket you can adjust using the provided lines). Five sizes are provided to accommodate a range of arm sizes.