Update:
I checked the roots of my Phal, and it turned out have quite some soft roots in the middle....
I cutted them all with some clean scissors, which I cleaned with some diluted bleach.....
Then I soaked the roots in some peroxide solution for a while and repotted it in bark/charcoal mix.

Did I do it right? Does the fact that most of the damaged roots were in the middle, will damage my flowers?