The classic phaser one mostly resembles an electric razor, a fact not missed by the cast and crew, and acted upon in an out take on the blooper reel where, after stalking menacing towards the camera, the men suddenly start “shaving” with their phaser ones.
Yes Virginia, there was a rising plate on the top of the phaser one. I still remember the early days at conventions how we used to debate the existence of this feature rarely high-lighted by any close-ups. Surprisingly this up-down plate shows up in the very first aired show “The Man Trap”.
In the scene where Captain Kirk and Mr. Spock beam down to the planet to find Prof. Crater. Captain Kirk says to Mr. Spock, “Set your Phaser on one quarter, I’ll leave mine on stun.” Mr. Spock thumbs his phaser one’s setting knob on top of his Phaser two and the hood pops right up.
The plate on the early black and white models were often a piece of brass plate painted black. Just behind and partly under 
it was a 3/4″ wide round Plexiglas rod. This is what most of us have been mistaking for the trigger bar. Behind that was a thin round knurled knob protruding as a thumb wheel. Opposing that were two plain paper squares glued to the body where, on later models, was a round lens for the read-out of the settings. The plate raised by rotating the thumb wheel with, well…the thumb.
As the knob turned, a link inside the body connected from the wheel to the round Plexiglas rod which would turn into the plate, forcing it to slide across the face of the Plexiglas rod and thus raise as it slid up. This action would raise the plate about 1/4″ because it which was hinged at the front and the rear part of this plate would ride up on the Plexiglas.
After the plate was at its fullest height, if you continued to turn the knob, a small Plexiglas rod telescoped out of the brass tube in the front and just below center on the phaser one’s body.
Only then at the very end of the rotation, at the highest setting, could you turn it a little further to light the light, or to fire the phaser one.
Design-wise, this means it could only fire on its highest setting!!But we know that it did fire on other settings for this was what we have seen on the screen.
These mechanical facts have been right in front of us for so many years. In the old paperback book “The Making of Star Trek” with those poor black and white photographs in it, the open phaser one has a visible knob, the link to the Plexiglas and the battery holder.
There was a small raised round aluminum button/rod on the bottom of the phaser one on some models. No one knows 
why it’s there. Was it a mock trigger? A knob to aid gripping the phaser one? (Very likely, as the little darlings were slippery) Or simply a knob to help remove the bottom when servicing it? Who knows? (Write me if you really do know, have ID and proof ready.) Update Below
The non-working models of both the pistol and hand phasers were mostly cruder than the above described. They had poor detailing, that is, when detailing was even remembered, and misshapen bodies, Velcro-glued for “invisible” holsters, etc.
Funny thing, I have some very clean pictures of a phaser one with a fixed, non-moving but raised plate mounted on it. Why? Maybe for a close-up model.
Well, that’s it, almost every detail known to human and Vulcan on the history of the black and white classic phaser one.
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UPDATE
This just in from:
Timothy Leming
Phaser details:
By the way, in the recently published book “Star Trek Sketch Book”, by Herb Solow, the sketches by Matt Jefferies indicate the knurled wheel on the phaser one was the sight adjustment knob, and the plate the was lifted when you turned the knob was the sight. The button on the bottom of the phaser one was the trigger! So you would raise the sight with your thumb and fire it with your trigger finger in a very natural position.
As I said before, the button on the bottom of the hand phaser was the trigger. The rectangular “ring” on the front of the phaser above the brass tube muzzle was the sight opening and on his sketch is labeled “clear” (as in you can see thru). The brass plate on top was simply the sight cover. The translucent piece that raised the cover was an illuminated sight screen. I guess the idea was you turn the knurled wheel, raised the sight, looked into the translucent part and it was like a lens that let you see thru the rectangular opening in front on the same line as the phaser beam would be emitted. It certainly goes a long way in explaining how they expected you to accurately aim such a small weapon. Evidently this is why there is a clear piece on the phaser 2 in front of where the hand phaser mounts. That way the sight on the hand phaser, that “looks” thru the rectangular piece on it’s front, is still usable when mounted on the phaser 2.
As to some detail on the pistol phaser, the aluminum ring on the muzzle that turns is the Range Adjustment Ring. The Lucite “beam emitter” on the muzzle, or “probe” as labeled on his sketch, is supposed to extend or retract with the adjustment of this Range Adjustment Ring.
The phaser 2 handle was definitely the power pack and the trigger was to unlock
only when the power pack was rotated into place.
Tim
I have not had a chance to check this for myself, but have also heard of it from a second person,
so I am putting this in as a foot note. ED.
