This reminds me of what happened to one of my first phals. I suspect that the plant has been overwatered, because of the bright yellow streak going down the center of that leaf and because, if you can zoom up the picture a bit, you can see that the leaf below the yellowing one is also looking wrinkled.
It might be a good time to take it out of this pot and see what's going on with the root system before you do anything else, just because it's possible that this plant may already be a lost cause. If the roots are green/white or yellowish in color and the texture of a fresh green bean, instead of black or brown and mushy, then go ahead and repot it and cut the leaf as advised above and everything will be fine.
If the roots are all black or brown and mushy, it's time to let this phal go. It might recover, but it will take a LONG time and if you are new to the hobby, it's easier to just let a phal in this condition go to the waste bin, rather than try to rescue it because recovery can take years.
Do NOT feel bad about that. It happens to all of us. Everyone on this forum has killed at least one orchid before. Go find another one just like it, or one that you like better and try again. Eventually, you'll get the hang of it.
Good luck! Here's hoping the roots look great and all you need to do is cut that leaf.