Phase prism is basically a shuttle, and moves around all units, even the colossus.
Warp-in works like this: AS soon as you have a Warp Gate you can warp in any unit to any place within the power of a pylon or phase prism. Once a unit is built, that warp gate goes offline for the amount proportionate to the time it would normally take to build that unit (from my understanding, a few seconds less actually, making the warp gate fundamentally important). Once that time is up you can instantly build any other unit, which would then take it off line and etc. Apparently Protoss players can use "w" or some future defined key to instantly select all their warp-gates.