Phal - cut, remove, or leave leaf???

[mayres]

I have a fairly large white noid phal that someone gave me that has a large diseased looking spot on the next to last leaf - actually, it has grown the last leaf while in my possession and the leaf with the spot was there (with the spot) when I received it. I'm concerned about the spot spreading - should I
1) Leave it alone and let nature take its course?
2) Cut out the spot with a sharp knife - clear to the middle of the leaf
3) Remove the entire leaf
I'm not crazy about doing surgery but if that is what I must do I certainly will. I've really no idea what caused the spot and if will spread and kill the rest of the leaf/plant in due time or not??? First photo is the leaf from the top and 2nd is from the bottom side.
Thanks - mike

[Cynthia, Prescott, AZ]

If it has been there for some time, I would be of a mind to leave it. You might take a permanent marker and put a tiny dot at the lowest point of the yellow. Then if you see that at a future time the yellow has progressed, you can at that point remove the discolored portion, or the whole leaf, as the plant seems to have enough leaf area to support the plant. The only place you don't want the discoloration to spread is to is the crown of the plant, hence, the spot on the lowest part of the discoloration. Cynthia