Black at leaf base/phal

[piaffe97]

Hello all! I'm having an issue that I've never come across before and not sure whats going on. I have a phal (which up until this point has been very healthy and thriving/bloomed beautifully for over 3 months). When the flowers became wilted and the stem started to turn brown I felt it was time to cut the stem down. The very next day the leaves wilted and looked pretty sad. And on day 2 after cutting, I go to lift the leaves to get a better look and they fall right off into my hands. At the base of the leaves it is black....looks almost like it was burned. Also black where the small stub of the stem remains, and black around the base of the plant where the roots start. Roots look now like they might be struggling a bit, but overall still green and at least living. No black found on them. Any ideas? Thanks in advance for any advice! Leigha