Speckled/mottled light green spots on phal leaves - magnesium??

[garnetscherzo]

Hi everyone, these spots appeared on my leaves a few weeks ago and haven't really spread much. The area where the spots are is slightly sunken, but not much. The undersides look ok, although the new leaf that's growing is developing a red tint on the underside. The spots happened at a time when my plant was in distress (another leaf was sick and then I got snow mold on my roots when I repotted, so the plant was not in potting media for a few days). I've looked at the St. Augustine guide to see what it could possibly be and I think it might be magnesium deficiency. I just repotted and I didn't see evidence of any pests or insects so I don't think that's what it is. It's not spreading so I don't think it's an infection. Any thoughts? What should I do?