When I hook my iPhone 6 up to my laptop, iTunes says my phone has 1.75 GB of free space, but my phone says i have no free storage left. Any idea how to fix this?

I hooked my 16 GB iPhone 6 up to my computer to check to see how much space I actually had on my iPhone after my phone said I have no storage left. iTunes showed that my phone has 1.75 GB of free space. I was wondering if anybody knew how to fix this and get my storage back. I don't know what exactly is taking up all my storage. Thanks!