A primary phaser coil is a critical component on board a Cardassian warship such as a Galor-class cruiser. The coil can be ejected, but doing so would leave the ship defenseless. (TNG: "Chain of Command, Part II")

The "primary" denotation suggests that there are secondary phaser coil(s) on board a Cardassian warship. The primary coil therefore most likely operates the large forward emitter as opposed to the smaller dorsal emitters.
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