Weird spot on phal leaf

[Fenix]

I noticed a spot on my left yesterday that is perfectly round and feels soft when touched, like the area is shriveling up. It has to more than double the size in 24 hours. Anyone know what this might be? And how to treat it? I've been trying to look it up but I can't seem to find something similar online. I'm thinking I should just cut it off since its spreading so rapidly.

[Roberta]

Since it is spreading and soft, I'd suspect a fungal infection. Yes, cut back to healthy tissue (a single-use singled-edged razor blade is best), then dust the cut edge with cinnamon.

[PaphMadMan]

Though it may hurt (you more then the plant) remove a good margin of healthy looking tissue too. The infection extends well beyond the visibly affected area.