Ah yes, true. Damn. I’m mixing up vampire stories. Anyhow, I stand behind the “spiritual creature, immune to all science” assertion, without my little sojourn into metaphor.
Phasers still disintegrate things just fine; they seldom use it at that level to conserve power.
Like others have said, it depends on the type of vampire. Some would die easy, others would laugh it off. It reminds me of an old story. Humanoid aliens fry all life on Earth - but are shocked to find human survivors. The survivors are brought on board and the ship heads for home so “The Masters” can examine them. Everyone on board starts having nightmares, and getting weaker and weaker. Some suspect the prisoners of being at fault, but can’t bring themselves to do anything even all the humans ( skinny, old, creepy specimens ) do is stare at them. Finally, the Captain demands an explanation from the apparent leader of the humans. Going by memory ( I’m probably butchering it ):
“The ancients knew how to deal with us, and did so well that their descendents did not even believe in us. Until you came, and your radiation burned away the stakes and the chains.”
“Nothing human could have survived what you did to Earth. Nothing human did.”
“Now; you shall continue on to your home world, where your people will meet their new Masters.”
I think those guys could handle a phaser. 