A lot of us don't keep some of them very long, so welcome to the Orchid Board!
Did this plant get moved recently, or has it been there for a while before it developed these patches? How fast have those patches developed? It could be sunburn, or heat damage from a light bulb, that hasn't fully developed.
I worry, though, that it could be a fungal or bacterial infection, like bacterial soft rot or brown spot. Sunburn or heat damage would dry to a light brown and the bad area wouldn't continue expanding. If it's a rot, though, it will probably keep progressing and you need to do something fast.
If you don't think it's a burn, cut off below the bad parts well into green healthy leaf with a pair of scissors. Sterilize the scissors before and between cuts with rubbing alcohol allowed to dry. This prevents spreading infectious organisms from diseased tissue to fresh. Don't let the cut pieces come in contact with this or other plants.
You can often take infected plant parts to your local agricultural extension agent, who will normally be happy to look at them under the microscope and try to figure out what it is. It's hard to recommend chemical treatment unless you know what it is.
The pseudobulbs are slightly shriveled, and I can't see your growing medium well. It is either not getting enough water, or the humidity is so low the roots can't supply enough water, or the roots are dead for some reason and dead roots don't supply water. A common cause for dead roots is old decayed potting medium. If your plant is in old decayed bark, this would make life harder for the plant.
It is not bad shriveling, so I would suspect not enough watering or low humidity. But, without knowing whether the plant has an infection, I wouldn't suddenly start soaking it a lot more often. You could gently pull the plant out of the pot and look at the roots and medium. If the roots are mushy and dead, or the bark is dark, wet and crumbly, that is part of your problem. You would need to repot into fresh medium. If the bark is still good, though, that makes me think even more of an infection.
Here is a good site for reading about plant problems, how to treat them and how to prevent them:
Orchid Pests, Orchid Diseases
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