iphone outgoing calls no ringing sound

When I try to make a phone call I cannot hear the ringing. If the call connects I can hear the person at the other end, its only the ringing I cannot hear. When have the headphones on, they work perfectly. I can switch to speaker and it works perfectly too.

This has only been a problem for 3 days. The problem does not coincide with an upgrade, however, since I got the problem I have taken the latest update (11.2) but it has not solved the problem.