A phase retraction is an energy phenomenon which can occur in some vessels' shields when power is transferred from one system to another.

Such a phenomenon was observed by Lieutenant Tuvok, chief tactical officer of the USS Voyager, in 2372, while engaged in combat with a hostile vessel in the Delta Quadrant. Noticing that, whenever the enemy transferred auxiliary power to their aft weapons systems, a slight phase retraction in their shields was the result, Tuvok conceived of utilizing a covariant phaser pulse to disable the vessel's entire weapons array, by firing at their aft control systems. (VOY: "Parturition")