A phase compensator can refer to an engineering tool or a component on Federation starships such as the Intrepid-class. They were also used by the Klingon Empire.
A phase compensator was one component of the plasma manifold aboard a Klingon Bird-of-Prey. (DS9: "Return to Grace")
During the USS Voyager's maintenance overhaul in 2377, Lieutenant B'Elanna Torres ordered that a new phase compensator be installed on a relay. (VOY: "Nightingale")
Later that year, when Voyager was trapped in the Void, Captain Kathryn Janeway gave Seven of Nine's favorite phase compensator to the Nygeans, so that they could repair their sensor array. (VOY: "The Void")