iPhone sound jack, only hear one ear

I read some users suggested to plug in headphones plug all the way down into a sound jack. I did, and still no sound in the left ear. But, when I move a plug in the sound jack the sound appear and disappear in the left ear. ( the right ear sound works good). I think the connection in the sound jack does not have a good contact for the left earbud. Any suggestion how it could be fixed. Looks like it is hardware issue.