Check your iOS version (Settings -> General) & make sure that you have either 9.1 or 9.2. The app works well with both of those versions on an iPhone 5.
If you do have either 9.1 or 9.2, try rebooting your device -- hold down the sleep/wake button at the top of the phone & the home button at the bottom simultaneously until the phone powers down. Then power it back up with the sleep/wake button & see if it works correctly.
If you still have the problem, you might need to do a device restore via iTunes.
Eat pecans - 10,000,000 squirrels can't be wrong.