Single den leaf looks like rot or fungus?

[Girl_With_An_Orchid]

Hello! I have a phal type dendrobium that’s go one leaf that looks really unhealthy. I noticed it started with a couple small black dots. The leaf then turned yellow and softened. I just removed it because it’s now half black and half yellow and very soft and bruised. The spots have spread a little down the stalk but nothing else is affected. I’ve attached pics of the leaf. I have removed the leaf because I was worried about any possible spread.

As far as care, it gets good light, more than my phals but not a lot more, and I water as needed to keep it a little wet but not soggy. I’ve got a small stick in the potting medium that I check regularly for that. It’s my first den so I’m hoping I’m right with that. It is a new orchid so I haven’t repotted it yet but what I can see of the roots is good. I have a new stalk growing so it seems to be fairly happy. Is whatever’s happening to the leaf going to spread?