Can't hear phone ring

There are two separate volumes on your phone. One is for your ringer and the other is for media. Is your mute switch on the side of your phone turned off? Try going into settings>sounds and see if the slider for "Ringer and Alerts" is all the way up.

If you turn on the switch for "Change with Buttons" You should be able to adjust your Ringer and Alerts volume with your volume buttons on the left side of your phone as long as music is not playing.