I noticed this today on one of my Phal's leaves. What the heck is it? It's not soft or anything like that and it's only on the top side of the leaf.
The Phal is already isolated due to the very yellow leaf tip it has on one of its older leaves. I know that they normally lose their older leaves, but the yellow colouration was so very sharp on this leaf that I decided to isolated and keep it monitored.