Why isn't my phone ringing when I receive an incoming call? It only vibrates. Have check Do Not Disturb and that is not on. It says something about the phone being in silence mode, don't know how to check that. What else?

Have an iPhone 6, just a week old.

My phone stopped ringing? It only vibrates and don't know why. Don't think I changed anything. Tried to find something in the support site it said to check Do Not Disturb, which I did. No half moon in the status bar. Turned it on then off again to verify I know what the status bar is. Then it said something about the phone being in silence mode. Where is "silence" mode?

What else needs checking? Called support, because I paid for apple care, but they are closed.