Black Spot that is turning leaf yellow
 

I have a phalaenopsis that I repotted approximately 2-3 months ago. In the past week it has developed a black spot that is rapidly turning the leaf yellow, but just the one leaf. I don't think it's sunburn since it has been cloudy lately and it doesn't get direct sunlight. What should I do?

The spot is a small bacterial or fungal infection and the yellow discoloration is the plant trying to fight off the infection.

If it were mine I would watch to see if it spread more or if it started spreading fast. If it was a fast moving infection then I would remove the entire area, not the whole leaf.

Brooke