On my airplay function iPhone is not listed as an option…how do I get it back?

I have an iphone 4S that has been great so far, however, about two weeks ago I started having problems with no sound on video and songs. The voice to the phone works, but it doesn't work for videos and audio. When looking at Airplay I noticed that "iPhone" is not listed as an option any more. It used to be. Has anyone any experience in this area or problem? What do I do? I have rebooted three times already and it was no help.