Iphone Storage & Itunes Storage Different?

Hi,

I have had this problem for a while now where my iphone says i have used 59.4GB of 64GB (4.6GB free), however my itunes says i have 17.11GB free. The problem is i keep having to delete items when i know that i have enough space - its like it needs a defrag!

I have searched forums and tried a couple of things but had no luck in solving this issue? Any ideas? I would like to stay away from restoring my phone if possible.

Thanks