You know, I haven't had this problem, but I have read of others who have. I think the consensus was that it wasn't really harmful to the plant. If it's not in full bloom, though, I think I would take it out of the media, wash it off gently, repot it in clean media in a clean pot. You could finish off by running hydrogen peroxide through it. And make sure you're not watering your phal until the media deep in the pot is approaching dryness and you keep it in a place with good air circulation.