phone not have audible ring when receiving call iPhone

Do you have the mute switch engaged? It's the little slider over the volume buttons on the side. If you can see orange, it's engaged. Slide it the other way.

. Ignore, please. A posting mistake on my part.

audible ring

Did you accidently put the phone in Canine Mode?

Occasionally my phone won't ring or vibrate when recieving a call. The ringer mute switch isn't turned on and the ringer volume is all the way up. I found that if I turn Airplane mode on and then turn Airplane mode off again it'll start working right again. It keeps doing this occasionally, any ideas what's going on with it ? I'm thinking it might be a operating system issue