From what I've been told or read on various forums, the real "internal" memory is reserved for the OS and other important files. It's hidden unless you get an "explorer" or file viewer type app. What it states as "phone memory" in SD card and Phone storage is really a part of the actual internal SD, but reserved for apps only.
Tho some apps load part of their over all data to the "internal SD", the "app" you download is stored in the "phone storage" This is done mainly for really big apps, typically games like Gun Bros. Some apps are fully self contained in just that file you download.