Phasers were energy weapons which could stun or kill, depending on their power settings. (PROSE: Mindwarp)
In one occasion, the Fourth Doctor complained about always meeting people "pointing guns or phasers or blasters" during his travels across the universe. (TV: The Horns of Nimon)
In 2379, "CD phasers" were sold to Thordon, where the Sixth Doctor got one exemplar from a Warlord; this occurrence led him to their source, Thoros-Beta. There, indeed, it was widely employed by the subordinates of Kiv, leader of the Mentors. Eventually, in a timeline, King Yrcanos killed Peri Brown with a phaser (called "liquifier" by him) as an act of mercy after her body was possessed by Kiv. (TV: Mindwarp)
While facing the threat of the Vervoids on the Hyperion III, the Sixth Doctor asked for a phaser, arousing the astonishment of his companion Melanie Bush. He secretly disarmed it, so later Doland couldn't use it against him. (TV: Terror of the Vervoids)
In the Federation universe, phasers were the preferred weapon of Starfleet personnel. On stardate 3368.5, in the late 2260s, the weapons proved ineffective against the CyberNomads. In 2368, the crew of the USS Enterprise-D found them equally ineffective against the Cybermen of the cyber-web. To compensate, the crew set their phaser rifles to randomised settings, the frequency of the beams constantly changing and not giving the Cybermen's personal shields the time to adapt. (COMIC: Assimilation²)
Alan Jackson noted how unrefined using vinegar was against the Slitheen, when compared to phasers and photon torpedoes. (TV: The Lost Boy)