(covers information from several alternate timelines)
Phaser banks referred to the phaser weapons mounted aboard Federation starships. (Star Trek: The Original Series; Star Trek: The Animated Series) They were utilized by Starfleet as early as 2233. (Star Trek)
Each bank contained one or more phaser emitters from which the beam energy was actually released but which shared common power sources and targeting systems.
The main banks were located on the lower half of the starship's saucer section, forward of the sensor dome. Additional banks were located on the ship's stern, above the shuttlebay. Port and starboard banks covered the ship's flanks. (TOS: "Arena"; TNG: "Datalore"; ENT: "In a Mirror, Darkly, Part II")
In the 2270s, a new system was developed, tying the phasers directly into the main reactor. While increasing phaser power, it had the disadvantage of cutting off most of or all phaser power if the warp core suffers an antimatter imbalance or if the reactor was damaged. (Star Trek: The Motion Picture; Star Trek II: The Wrath of Khan)
On a schematic of the Galaxy-class USS Enterprise-D, the location of the phaser banks was labeled. The dorsal of the primary hull featured an upper phaser bank. The dorsal secondary hull had two phaser banks located on either side of the aft torpedo launcher. The ventral secondary hull had a lower engineering phaser bank and, aft of this bank, more phaser banks. (TNG: "New Ground")