Mold/ fungus/ bacteria in the medium?

[Sofifi]

Hi there,
Several of my phals have recently started to develop something white in the medium which I don't know how to threat or prevent.

I don't have enough posts to post photos yet, so here are they on my Dropbox:

https://www.dropbox.com/sc/8xh9qox561sd7xv/OmdOrcirdR#/

I've repotted 2-3 months ago for the same reason and now it's started again.
All phals are in great condition, lots of new roots and/or leaves, no other damage.
I don't know whether to repot them again or threat them somehow.
Maybe there's not enough drainage... Anyways, your help is much needed guys!:-)

Thank you!