Phal flowers wilting and falling off, black on undersides of leaves

[Zoi2]

If it can be rubbed off it sounds like a mold. I would take the plant out of the pot it's in, clean the leaves with brown listerine or alcohol, sterilize the pot and repot in new potting medium. You do not want to transfer mold spores to the new medium.
Joann

[nibbler]

Dont worry about it. 4 of my phals came with a fungus when I bought them. spray the roots with a systemic fungicide. I think Physan 20 or phyton 27 is what the others use in the US. Cut off any squishy roots and put a tiny bit of cinnamon on the end of the roots (Do not sprinkle it across the root, which was my first mistake) Repot it in bark in a clear plastic so you can see the roots. I normally stick my finger down into the bark, if it feels in wet or very damp I leave it alone.

And I would suggest youtubing how to replant a phal. I think I left mine too loose and I am going to have to repot them all tomorrow night.