Along with no trigger guard, the phaser pistol had no sights. I wonder how hard it would be to shoot accurately. (When seconds count, your redshirt cannon fodder might be minutes away.)
There's a frame in "Return of the Archons" where Kirk is firing his Type I phaser, and the beam is going where his eyes are looking, not where the weapon is pointing.
Maybe hand phasers don't need sights because they have a sensor that looks at your eyes and figures out what you mean to be shooting at. Then the nozzle tilts itself to aim for you. Fighter pilots have something like that in real life now.