Phal bacterial infection

[lauraeli]

Second year in a row I had to cut two leaves off one of my mini phals due to a bacterial infection. This is actually the 3rd time this particular phal has had this issue but none of my other phals have had it. Any reason why a single phal might be prone to it, and anything I can do to help prevent it in the future?

All of my phals are in the north window. Last year when it got infected, it was in the east window. The roots are very healthy, it's potted in sphagnum. I water it on an as-needed basis which lately is about every 3 days. I have a fan on in that room constantly.

Here are some pictures of the leaves I removed