If I do my math that's a yield of 8.673 kilotons of TNT... I could be off by a few digits but You'd think you'd see a huge explosion...
If there was a huge explosion it would not be a safe weapon to use like that for Starfleet personel, who seem to use phasers at walls of rock only a few meeters away from themselves. A huge explosion would probably stop use of a phaser for such a task at any easy to see range. Though that does make one wonder about ship's phasers or the phaser cannon used in The Cage.
Even that "field piece" or "industrial drill" seemed to be safe for use at short ranges with minimal precautions (goggles!). And when the space jellyfish bombarded the Bandi Old Town in "Farpoint", Yar and Data commented that it felt much like standard phaser bombardment. Essentially, what they experienced (when moving back to the surface, and at ranges of a city block or less) was pressure waves that shook things up a bit, but no heat blast, no shrapnel, and no weird radiation effects or the like. When in later episodes the E-D uses her main phasers for drilling, the process seems very gentle and creates few if any secondary effects in the immediate vicinity. Timo Saloniemi