Chris Breitner wrote:

Hey Everyone. I can't seem to find the answer and/or product to
satisfy my needs: a phantom power filter/remover.

I have a ribbon mic I'd like to gig with, and the PA systems we use
normally plug into have an all-channels-on/off for the phantom power.
Our vocalist uses a condenser mic, so she needs it on. If the phantom
power hits my ribbon mic, it might permanently damage the ribbon
element.

Does anyone know of a DIY homebrew solution?

You've gotten plenty of good advice so far, but the one thing barely
mentioned is that besides a center-tapped output transformer, a
defective microphone cable is just about required in order for phantom
power to damage a ribbon mike. So buy yourself a nice $25 mike cable
that's a different color than all your other mike cable. Treat it
gingerly and label it "only for XXX ribbon mike." Don't let anybody
step on it, tug on it, tie it in knots, or run it over with a rack full
of heavy equipment. This will cost a heck of a lot less than a good
isolation transformer.

ulysses