Phasers are a type of advance laser weaponry.
Phasers work by having a typical laser, but the photon frequency of the laser is made to change its frequency or 'phase' in a cyclic fashion, making it more dangerous. While lasers are better at piercing shields than most other types of energy directed weapons, they are less effective against matter. Phasers do not have the same weakness, or the level of it.
Appearance varies by species/manufacturer.