Silenced calls

There are a few settings that can silence the ringer on the iPhone. If you check Settings>Phone>Silence Unknown callers. That will silence calls from people/numbers that are not in your Contacts. Do Not Disturb will silence all notifications of calls, iMessages, etc. Check that in Settings>Do Not Disturb. And finally, there is a Mute switch just above the volume buttons on the side of the iPhone. With that on, the ringer will not sound, but you should receive a vibration if you have that turned on. If the switch is up towards the screen Mute is off, it it is towards the back and you see an orange color when looking at the switch, then mute is on and the ringer is silenced.