Welcome to the Orchid Board!
Listerine contains alcohol, which may damage roots. Damaged or dead roots may be colonized by fungi that specialize in growing on dead plant material. That looks like what you have. Such fungi do not invade nor harm the living plant.
Most problems growing in a home are due to suboptimal growing conditions. Infections are not common, and usually due to suboptimal growing conditions.
Let your plant stay dry between waterings for a day or so. When dry the roots become silvery white. This will help control mold.
I would not use Listerine nor other alcohol formulations on roots.
What are your growing conditions? Phals. prefer being warm to hot, in full shade. Higher humidity is better, but hybrids tolerate lower humidity.
For more reading on Phals., click Forums in the left yellow menu. Then Beginners. Near the top is a sticky thread, The Phal. abuse stops here.
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