Phone storage usage different on iPhone vs Mac

I synced my 16GB iPhone 5S to my Mac today and iTunes said that there's about 2GB of empty space left, as shown below.

But when I went to Settings>General>Usage after the sync, it said that there was only 713MB of space left on the iPhone. I tried re-syncing but nothing changed. I did not add anything new to the phone during either sync.

Is there anything wrong with my phone and if so, how can I fix it? Thanks 🙂