To me it looks like a fungal infection. How long ago did you notice the damage? Anyway, you should probably treat the spots with an anti-fungal agent, perhaps physan 20, or at the least a dusting of cinnamon, which has anti-fungal properties. Remove it from proximity to any other orchids and watch it carefully and do not overwater or mist the foliage. Anyone else?
Good luck!
Remo