The phase-pistol was a type of phase-modulated energy weapon, a personnel sidearm characterized by a focused energy discharge in the form of a steady stream or a phase pulse. It was introduced in 2151 for use by Starfleet personnel as a replacement to the EM-33 pistol. MACO utilized a different model of phase-pistol. (ENT: "Broken Bow", "United")
The phase-pistol was equipped with two settings: "stun" and "kill". (ENT: "Broken Bow") The former could also be used to ignite a fire. (ENT: "Desert Crossing") The temperature to which the weapon was capable of heating a liquid was at least 398 degrees. (ENT: "Civilization") It could be utilized in clearing obstructions of rock and earth, and as a cutting tool, its beam capable of slicing neatly through an enormous trunk. (ENT: "Terra Nova") By cross-polarizing the power cells to increase particle yield, the weapon could be modified to be more effective against shields. (ENT: "Regeneration") A phase-pistol could also be set to overload and function as an explosive device. (ENT: "United")
Although phase-pistols handled similarly to an EM-33, they were different in that they did not require the user to compensate for particle drift, but to instead point straight at the target. (ENT: "Fight or Flight", "Sleeping Dogs") The effects of a phase-pistol hit also differed from those experienced with other weapons of that era. 22nd century Suliban and Coridanite weapons inflicted identifiable wounds, tearing through clothing and into the victim's flesh. (ENT: "Shadows of P'Jem") The phase-pistol, however, was capable of having an effect more comparable to an electric shock, capable of causing severe injury without breaking, burning or otherwise damaging the skin. Along with the beam, a pulse would surge through it, causing more damage. (ENT: "Broken Bow") It was also capable of making the rounds harmless for training purposes, possibly by setting the weapon to stun. (ENT: "Sleeping Dogs") However, it was possible for phase-pistols to inflict wounds. (ENT: "Demons")
Crewmembers from Enterprise NX-01 first used phase-pistols in April of 2151, when Captain Jonathan Archer infiltrated a Suliban helix. Aboard the helix, Archer was able to stun a Suliban soldier before having his own phase-pistol turned against him by Silik. Due to bizarre temporal effects within the helix's temporal chamber, however, Archer was able to literally dodge the phase-pistol beam and escaped relatively unharmed, while the beam's presence in the chamber caused a large shock wave to surge through it, as Silik had said it to be unwise to use the weapon in that room. (ENT: "Broken Bow") Enterprise carried a total of fifteen phase-pistols on the ship during 2151. (ENT: "Shadows of P'Jem")
Ensign Masaro committed suicide with a phase-pistol in 2155. (ENT: "Terra Prime") Starfleet phase-pistols were used as late as 2161, when an away team from Enterprise fought against a group of aliens on the planet Rigel X. (ENT: "These Are the Voyages...")
MACOs used a different model of phase-pistols as their primary sidearm. The pistols were similar in appearance to the EM-33 pistols, and were designed to fire blue phase pulses, essentially bolts of energy, instead of beams like those fired by their Starfleet counterparts. The pistols were also equipped with both "stun" and "kill" settings.
In 2154, Talas was shot with a MACO phase-pistol set to kill. Although she was only grazed, she, being an Andorian, was especially susceptible to phase-pulse infection, and subsequently died of her injuries. (ENT: "Babel One", "United")
The Tellarite captain-turned-bounty hunter Skalaar utilized a type of phase-pistol when apprehending Jonathan Archer. It is unknown if it had any settings, as Skalaar only used the weapon to stun his targets. (ENT: "Bounty")
Although similar, phase-pistols were not yet technically phasers. According to Worf in TNG: "A Matter of Time", phaser weaponry was invented in the 23rd century. Phase-pistols were intended as an earlier version of phasers according to the text commentary on ENT: "Broken Bow". Even though Enterprise carried both EM-33 and phase-pistol weapons when it was launched – with both being used during "Broken Bow" – the EM-33 pistols were not used by the crew again. The phase-pistols used by the MACOs in seasons three and four were re-used props of the EM-33 pistols. The MACO weapons were identified as phase-pistols in "United". Based on "In a Mirror, Darkly, Part II", the phase-pistols were not powerful enough to vaporize or disintegrate a person like a phaser could.
In 2002, Art Asylum produced a phase-pistol toy available at most toy stores at the time. The mold was so accurate that, although approximately twenty percent smaller than the prop created for the series, the producers of ENT ultimately used the toy versions as on-screen props, for stunts and, in some cases, for full-on "hero" shots. They were repainted because originally – i.e., when the Art Asylum toys were released – they were not the same colors as the phase-pistol props used already on the set. While original "hero" props were built for US$2,500, the toy version was priced at just US$20 and came bundled with a communicator. At a convention, actor Scott Bakula had an opportunity to pose with one of the toys and he apparently said that it felt even more realistic than the prop version. (citation needed • edit)
Several prop phase-pistols were sold off on the It's A Wrap! sale and auction on eBay.  The MACO pistol was called a hand gun  and a plasma gun  and was, in some cases, still identified as an EM-33 energy gun  in the auction.