A phaser emits a singular, straight, laser-type beam from the point of fire to the target.
It can be set to varying degrees of intensity. At its lower settings it can stun victims('set phasers to stun') or render them unconscious. At its higher settings it can kill('set phasers to kill') or even vaporize.
Outside of its combat uses, a phaser can also serve as a cutting torch, capable of cutting man-sized holes in metallic walls; a welding torch, capable of welding two pieces of metal together; and a powerful heat source, capable of heating, at one of its lower settings, a rock.
The phaser can also be made to explode by setting it to overload. The phaser will emit a high-pitched squeal, increasing in intensity, until it explodes like a grenade. Doing this allows the phaser to be used as a time-delayed explosive or distraction.