Hi and welcome to iMore.
Does the phone in all other respects make a noise? Can you go to the ringtone page in the sound menu in settings, click on your desired ringtone and hear it from there?
Have you tried setting a different ringtone and made sure the mute switch isn't on too?
I know these are simple questions but it helps us troubleshoot and sometimes it is the most easily overlooked answers that get results.