android storage issue

So i have a hTC EVO LTE and at times I get a "SD is full" message when I still have little over half left on the 32GB card. Well then today as I weas cleaning off crap I don't use much, I came across the "move" option I eirther have "move to phone storage" or "move to internal storage" but no "move to SD" option.

So my questions are. What could be the casue of the SD is full message and what exactly is "phone storage" and "internal storage" ? Its becoming a real headache having to manage all of this shit. Just give me an Android phone with 32 or 64Gb of storage bulit right in. Then we wont have to deal with this mess. most phones can only support up to 32 or 64GB so there really isnt a need for a silly Sd card.