The phantom has a set of "Bellows" in the tail cone, you can see the air inlet on the tail (No, it's not two pitot tubes, the lower one is for the bellows) but as the aircraft goes faster and more air is forced into the bellows, it will add friction to the controls. This was to help the pilots not oversteer the aircraft and throw it out of the flight envelope. It's an all hydraulic system, so the regular forces present on cable and linkages do not apply (as much).