A phaser burn was a type of burn caused by a phaser.
In 2368, Jean-Luc Picard stated that there were no phaser burns found on the hull of the SS Vico, to which Data stated that the evidence pointed to a disruptor-style weapon attacking the Vico. (TNG: "Hero Worship")
Later on, Jason Vigo suggested to Bok that he could create a phaser burn on his shirt and send it to Captain Picard, to try to convince him that Bok had killed him. (TNG: "Bloodlines")
Later on, a holographic version of The Doctor programmed by Seska tried treating Tom Paris for a second-degree phaser burn and instead gave him 20ccs of nitric acid, "a proverbial salt in the wound," according to The Doctor. Following this incident, Paris sarcastically suggested to Tuvok that they could next go to the mess hall and have the holographic Neelix burn his arm with a frying pan. (VOY: "Worst Case Scenario")