It’s interesting that it’s a middle leaf. Our orchids tend to grow new leaves on the top and drop leaves on the bottom as they put out new roots going up their stem. Every few years I have to unpot them and cut the bottom few inches, otherwise they will climb out of their pot.

When our orchids drop leaves they look very similar to the leaf on your plant.

In my experience, this variety of orchid thrives on benign neglect. Ours very rarely get fertilized. They also only get watered every two weeks or so and when they get watered the bark they’re in is pretty well saturated.