This phal recently released a spike, but the spike has stopped growing (it's just a stub, less than 1/8"). Upon closer inspection I noticed that it has developed a jagged texture and is starting to get purply. There are very small dusty-looking things on a couple of the roots that fall right off when I touch them; I don't think they're dust. The leaves are also a little bit floppy to the touch.

This must be some kind of parasite. I'm not going to try to nurse the plant back unless someone thinks there is a reasonable chance of success. But does anyone know what it is so that I can try to avoid it in the future and/or take steps to protect other plants?