But there's absolutely no reason to think that phasers have anything to do with photons.
Generally speaking, we could argue that all or at least most real-world weapons are simply too primitive to be of any significance in Star Trek. Certainly "shields" is a scifi concept that can easily and categorically negate all known weapons if need be - and then be countered by an unknown weapon, one specifically dreamed up for its potency against shields.
More specifically speaking, the dreamed-up weapons and defenses of Trek are indeed extremely potent. From "A Taste of Armageddon", we know that the offensive weapons of a single starship of the time can reduce (from our viewpoint pretty advanced) planetwide civilizations to slag and ashes in no time flat. Yet we also know that those weapons barely dent other starships, and that space warfare of the time doesn't much involve slagging of truly advanced enemy planets. One can then easily infer that the weapons we know or dream of today wouldn't do squat in Trek wars.
Indeed, it would be pretty poor drama if a weapon we currently consider "awesome" were regarded as awesome by our future Trek heroes as well. It would be as cringeworthy as our heroes appreciating a clumsy VR helmet and glove (TNG "Interface" really suffered from this) or thinking that the most recent 21st century findings of cosmology are still cutting edge science in the 24th century (I'm afraid Christopher Bennett's otherwise cool novels in turn suffer a lot from this). Or akin to Dirty Harry being impressed that his carriage is horseless, his revolver is double-action and smokeless, and his telegraph wireless and portable within his horseless carriage.
Timo Saloniemi

I like that, Timo. Good line.
That said, although it is totally beyond our engineering ability, we know with near certainty how an antimatter explosive would work. Phasers are likely to be similarly or less powerful (and more accurate, controllable, etc.). On the plus side, a few dozen or hundred antimatter warheads of TNG manual size would certainly be capable of reducing any 21st-or-so-century-level society (as the one depicted on Eminiar) to ruin.
Presumably actually advanced civilizations have much better defenses (i.e., any) against orbital bombardment from a starship, but we can say without any fear of contradiction that in the absence of something that stops photon torpedoes from detonating near the surface, a single starship is still fully capable of wiping out the majority of the populations on Earth, Romulus, or Kronos.
Maybe a hundred times as many thermonuclear weapons could do the same thing, definitely more cheaply and without the (apparently minor) hassle of weaponizing dangerous antimatter--the magnitude of the defenses is the only thing that might make nukes impotent, and their demonstrably lesser cost might make them much more effective as swarming weapons when expensive pho-torps or Q-torps would be economically unsound. Further, I'd submit that, say, some random minor colony on New Timbuktu would be just as dead from the deployment of a thermonuke as they would be from that of an antimatter weapon--at a fraction of the cost.
Iirc, a thermonuke is going to have roughly 1/2000th the power of a comparable-sized matter/antimatter bomb (perhaps even less, given that much of the yield of a thermonuke is actually driven by neutron flux striking quasi-fissionable material). That's quite a differential, but all the conventional arms aboard a fully loaded B-52 combined are less than 1/2000th the power of a megaton thermonuke, and I personally would still consider a B-52 quite awesome... despite being the Excelsior-class of our time.
Spock can call them primitive all he wants. H-bombs work quite well. Heck, I'm of the opinion that a Romulan "plasma torpedo" is merely a fancy-future name for nothing much more sophisticated than a Ulam-Teller device, probably on the same scale as the Tsar Bomba--a mechanism
quite competitive in yield with the photon torpedoes as outlined in the TNGTM, if somewhat bulkier at 27 tons compared to (guesstimating) 500kg-1 metric ton for a pho-torp.