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")
In 2370, 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")