Phal with black spots on leaves

[piaffe97]

I've recently noticed these black spots spreading from the leaf edges towards the center of the leaf and I'm not sure what's going on! Here's the plants history: I bought it a year ago in full bloom. After a month the flowers dropped, and just this past February it popped out 2 more flowers since I never cut the stem down. It was planted in the same moss it's in now, and the same pot.

Growing conditions: it's about 70º right now, day and night. Humidity is good. I let it dry completely between waterings, average once every 10 days. I use Dyna-gro fertilizer (7-8-6) each time I water. It gets good light, sitting about 4 feet away from a brightly lit window. No direct sun, but plenty of indirect.

The black spots are mostly on the leaf surface, but I've noticed some underneath as well. I also want to point out the roots, in the moss they look great, but the surface roots look burnt! Any thoughts?