EEK! Just found brown rot/erwinia on one of my Phals' leaves... :/

[tom_e_boi]

I was checking up on my phals, like I do multiple time throughout the day and everyday, and I couldn't believe it when I seen this brown rot on one of the lower leaves of one of them. What surprised me was how big the spot was. Thankfully, it looks like it started on the outer edge of the leaf and didn't make it to the crown of the plant. I used sterilized cutters to prune the leaf and disinfected the space around it.
I've encountered this problem before, but never with any of my 'chids. I'm pretty sure that I've done a thorough job of cleaning and disinfecting the plant and I've isolated it from my other phals so that it won't spread to any of them. I was just wondering about what causes this to happen? And if anybody else had any suggestions that they'd like to share. I'm also studying up on it right now, but I'd like to hear from others on here too.
I never get any of the leaves wet, splash water on them, or anything like that. Plus, they get excellent air circulation from my ceiling fan too. Like I mentioned earlier, I'm constantly checking on them several times a day everyday, so this brown rot is very recent and boy does it like to spread fast. Hopefully, I caught the problem in time, before it got any worse. So I'm keeping an even closer eye on my 'chids, with my fingers crossed.