Phal with spots on underside of leaf (top seems OK)
 

http://i716.photobucket.com/albums/w...leaf-spots.jpg

This plant had some root rot that was cut off and has been growing new roots. It actually seems to be quite active at that, with a couple more new root tips appearing on the lower crown. It also had a fungus gnat infestation that was recently purged.

What might be the cause of these kinds of spots? They're actually subtle when looked at with direct light. In this photo, they're enhanced by the light coming in from behind. The top part of the leaf doesn't show these spots.

Just bumping you post as I'm afraid I can't help :(

:bump:

Thanks, Rosie.

I forgot to mention that it was put outside for about 2 weeks. Temperatures were pretty normal.

Anyway, the phal has been inside for a few days now and I don't see any further progression... hopefully that'll be it, as the plant has a new spike growing.

I would say it from dew and cold weather. Water drops accumulated on the leave and got too cold and the cells started to break down.

^ Thanks, Keith. :) That makes sense to me... the leaf turned forward a bit, so that some of the underside is easily exposed to water droplets falling from above. And a couple of the nights dipped down to about 50F.

What Keith says sounds right if it's been outside. I've not seen it before, but I've heard of that type of thing happening.

I would also think the same, especially if the spots are not spreading. Still worth keeping on eye on for a while though, just to be safe.

Consider wiping the spots with a damp cotton ball. If the cotton ball comes away with specks on it, then you may have critters. If not, it may be as everyone says above.