Question: What Are These Black Spots On My Phalaenopsis Leaves?
It depends. Some phalaenopsis have naturally mottled leaves, so it may be natural coloration. However, leaf spotting can also signify a bacterial or fungal disease. Bacterial leaf spot is fairly common among orchids, and it can be aggressive and dangerous on phalaenopsis. Similarly, fungal disorders an cause leaf spots, especially if the plant is left exposed to moisture on chilly nights. Treat these conditions with Physan, baking soda or copper fungicide.
Larger black spots can also be caused by sunburn. If areas of direct exposure to sunlight turn yellow, then black, it is most likely sun damage. Cut away the affected areas and disinfect your plant. The very best defense against leaf spot is good hygiene and safe watering practices.