Help! My phalaenopsis' stem appears to be rotting!

[mfaircloth]

Okay so

I have had this phal for 4-6 months. I bought it while it was in bloom. Since I bought it, it has grown quite a lot, with many new flowers in bloom. It has two stems, or flower spikes. I'm not quite sure what they're called.

Several days ago, I noticed that some of the flowers were falling off. I have 3 other phals so I knew that this was normal. Today I came home and noticed that 3 more blooms had fallen off. I thought this was strange because in the past they have fallen off slower and one at a time. Upon further inspection, I noticed that all of the flowers were only falling off one of the stems/spikes. I then noticed that the two stems were different colors. I went to touch the "bad" stem and it was mushy and the outer layers basically came off. The stem/spike in question is a brownish color while the other, is a nice healthy looking green. The bad stem/spike is mushy, gross, and brown all over. It appears to be rotten.

I thought that the best thing to do would be to cut the stem off right at the crown, but I am now worried about the rest of the plant. I am a beginner so I need some help! I googled rotten orchid stems and spikes, but the only results were about rotten orchid roots. The roots, leaves, crown, and other stem/spike on this plant seem to be healthy.

Thanks for any and all advice that you can give me.