You can use two pretty large caps in an inline-blocker, and two bleed-to-ground resistors on the microphone side of the caps.
OR...
An alternative inline blocker, with a transformer in it.
Plug the blocker in and wait a minute or two if it's the cap/resistor variety. Then plug in the mic.
Doing this, I cannot conceive of a single circumstance or situation where it is AT ALL POSSIBLE for phatom power to damage the microphone, assuming that the phantom power remains constantly-present.
If you can't reasonably rely on the phantom being constant, (easily-nudged phantom switches, power cuts etc) then all bets are off, and you are risking your ribbons just by being in that room!
That's my take on it, anyhow!
keith