You need ->
1. Two PHX plates. (PHX 2x2)
2. Wire hydraulic.
3. A button.

Spawn your first PHX plate on the ground and freeze it.
Spawn your second PHX plate above the first PHX plate and freeze it.
Take out your Hydraulic and make a hydraulic from the first plate to the other plate.
Now, spawn a button with TOGGLE on.
Ok, lets say the hydraulic was 500 in length. Make the button: ON = 400 and OFF = 0. That way the plate will be 100 units under the second plate when the hydraulic is on.