Thank you for using Apple Support Communities!
I would like to recommend 3 things. If you have not already, I would restart the iPhone.
iPhone, iPad, iPod touch: Turning off and on (restarting) and resetting
Restarting your device
- Press and hold the Sleep/Wake button for a few seconds until the red "slide to power off" slider appears, and then slide the slider.
- Press and hold the Sleep/Wake button until the Apple logo appears.
If the issue persists, then from that same article I would reset the phone.
Press and hold the Sleep/Wake button and the Home button together for at least ten seconds, until the Apple logo appears.
And if the issue is still not resovled, then I would backup the phone to iTunes, and restore it.
iOS: How to back up and restore your content
All the best,