Did you ever edit your host file for any reason? What troubleshooting steps have you taken? Have you tried a hard reset, or reboot? Hold the top power button and the home button at the same time until the Apple logo appears, then release. If this doesn't work, you may need to restore to factory settings. Back up your phone first. If not in iTunes, then in iCloud. If you can't restore through iTunes, then go to Settings>General>Reset> Erase and reset all Settings . You might take your phone to an Apple Store and let them look at it.
Sent from from my ancient but trustworthy iPhone 5