"The Wrath of Khan". Phasers at low power and close-range left scorch marks (at the weakest) and shallow cuts which would be difficult to make out at the size Excalibur was displayed at in the original FX.
...But the casualties were apparently limited to the spaces directly affected by the shallow cuts. To reproduce these effects in large enough scale to kill the total crew of a Constitution
class vessel, M5 would need to hit basically every square meter of the surface, and even that would only get the people in the outer parts of the ship.
And IIRC, in "Basics" the backup phasers were overloaded and discharged inside Voyager, stunning the Kazon crew in one go from the inside of the ship and through the bulkheads.
I had forgotten all about the nuances of that trick. But it would seem to be an internal power surge type of affair, rather than something directly relating to the properties of phasers. That is, it could have been the backup shield generator power couplings that were sabotaged, too. Or the backup holodeck power couplings. The result would have been the same. And it still wasn't lethal for all the Kazon...
Incidentally, how did Kirk know to ask M5 to scan whether there was life aboard the hurt ship? He had not had the chance to do any scans himself, and the radio chatter had not revealed particularly extensive casualties. If M5 truthfully answered "25 people dead, 402 alive", Kirk's accusations of murder would sound hollow, as his question was about absolutes.