Cannot hear music on my iPhone 5S
Hi and welcome to Ask Different!

A few things to try:


Make sure the mute switch is off and working - on the top left side of the phone there's a switch that has a red backing if it's turned on. If it's showing red, toggle it back, and your sound will come back on. Simple :)
If that does nothing, make sure the switch works. Toggle it back and forth a few times, there should be a popup indicating that sound is now muted. If nothing appears on the screen when the switch is toggled, the switch is probably broken, and you'll need to talk to Apple or your carrier's insurance about getting it fixed.
I'm guessing you already tried this, but there are two volume settings on iOS, one for the ringer and one for apps and music. If you just use the volume rocker in most places, your ringer volume changes. If you use it while music or sound is playing, app volume changes. Make sure that your music/sound volume is up.