iPhone 5 ringer is off

You posted in the iPad forum instead of the iPhone forum. To get answers to your question, next time post in the proper forum. See https://discussions.apple.com/index.jspa I'll request that Apple relocate your post.

 Cheers, Tom 😉

There can be any number of reasons. Check the mute switch on the side of the phone by the volume switches. Make sure it is in the up postion, no color showing. Also, go into Settings>Sounds makes sure the volume is up and that a ringtone is selected.