I would say it's either a bacterial infection or a leaf spotting fungus. I'm leaning towards bacterial. Cut off the worst leaves and start treating the plant with Physan 20 once a week for 3 weeks. It's a mild bactericide/fungicide. Put the plant in an area where there's good air movement and don't hang other plants above it where they might drip on it. One more thing, and this may just be an isolated experience for me, but that kind of problem pretty much disappeared when I increased the amount of calcium and magnesium that my orchids got. Either use a fertilizer that contains both of those, often called a cal/mag fertilizer, or use a supplement. I use a supplement called MagiCal twice a month. It's just a suggestion but use the Physan 20 for sure.