A phaser bank was an area on the external hull of a Federation starship where phasers were mounted. Phaser banks were equipped aboard starships by the 2230s, and continued to be mounted until the introduction of the phaser array in the mid 24th century.
Constitution-class starships were equipped with four phaser banks, each equipped with two emitters. The primary phaser bank was located on the lower part of the saucer section. There was also a bank located at the aft of the vessels, located above the shuttlebay, and a bank on each side of the saucer to guard its flanks. (TOS episode: "Arena"; ENT episode: "In a Mirror, Darkly, Part II")