My volume says headphone and I can't hear anyone on phone unless I use speaker help?
Make sure there isn't any dirt or pocket lint in the headphone jack, if there is something in there it could be causing connection problems.
Try disconnecting and reconnecting the headphones 5-6x or spraying compressed air into the jack.
You can also try restoring the iPhone.
If that doesn't do it, you can setup service for the iPhone online or have a Genius take a look at it.
Retrieving data ...