In TOS, all phaser fire that was seen came from the ventral saucer, either the forward and sometimes the port/starboard sides (phaser pulses). In the TOS Movies, only the Enterprise's ventral saucer forward and ventral saucer port phasers are fired.
As to whether they had dorsal phasers or not is purely up to your imagination. I'd like to think that the TMP Enterprise's phaser locations correspond to the TOS Enterprise's phaser locations.
In dialogue, the TOS Enterprise had Forward, Port, Starboard, Midships and Aft phasers.