The rear of the Phantom appears to drop down, but this is an illusion created by the belt and window line. The roofline maintains its height. The massive C-pillar serves to hide celebrity occupants from the public eye.
The rear doors open from the front, creating a look of accessibility to the cabin when both sets of doors are open. Because this style of door makes the rear ones a little difficult to close from inside, there are buttons on the insides of the C-pillars that automatically pull the doors shut.