I had a similar problem a week ago. The audio was very low even with the volume control at it's highest. I would have to put the speaker directly to my ear in order to hear anything- there was more of a "static" sound than actual audio.
The only thing I could do was take my iPhone to a Verizon store. They quickly diagnosed it, determined they couldn't do anything about it either, and ordered a replacement for me (My phone is under warranty- if you have Verizon it should be a year warranty as well.) It took 2 days to receive the replacement in the mail. So everything is peachy now.
I suggest taking your iPhone to a Verizon store and get a replacement. Im sure it is a manufacturer's defect, so take advantage of the warranty if your phone is still under it! Just be sure to send your original phone within 4-5 days or you will be charged an arm & a leg for it.