Itunes not syncing all my selected songs to my iphone?

I have 2, 000+ songs in my library and they all dont fit on my phone, i can fit about 1, 100 when i start syncing it says that i have 1, 100 songs ready to go on my phone, once its done syncing it says i have 600 songs on my phone please help

This is EXACTLY why iPhones come in 3 sizes:

16, 32, and 64 GB.

TIP: Next time you upgrade your iPhone, choose the 64 GB Model, or, the 128 GB Model, if available.