Possible Phal rot

[Orchidpablo]

So I have this phal that I bought at the local grocery store and it was very healthy. It had two sprays of pretty small purple flowers. The flowers dropped, which was normal, and so I cut one of the stems back to the first node before the first flower to see if I could get a keiki to grow (or at least some more flowers), but the end of the stem where I cut it has turned black.
And the other stem, which had more unopened buds and thus took longer for the flowers to drop, the little sheaths where the flowers come out have all turned black and the sheaths along the nodes are turning black as well.
So to make a long inquiry short, What is going on here? Should I just cut the whole stem off or what? I'm afraid it might be rot, but I don't have a clue what from...
I'll attach a picture to give you an idea of what it looks like.