White mould+yellow leaf after repotting

[Julia17]

Hey everyone, I'm new to this forum. Hoping to get some opinions about what's happening to my Phal and if it's salvageable.

Quick history: I've had it for almost a year, got it for Valentine's day last year (which is why I really want to save it!!). It was planted in sphagnum moss and it got a fungal infection a while ago so I treated it with fungicide and repotted it. It had a lot of rotting roots so it received a hefty trimming.

I repotted it in a mix that was pretty much all bark I think, has some tiny pebbles as well. It has been getting new leaves but it wasn't looking GREAT and it was always very very dry and had no stability whatsoever. Like the idiot that I am, I repotted it last week and added some sphagnum moss to retain a bit more moisture. I don't think it was sterile because literally within a week I noticed fungus growing. Now my biggest leaf has gone fully yellow and looks like it's going to drop.

It has barely any roots apart from the long aerial root you can see in the photos.

Today I used fungicide on it and left it in the sun for about 20 minutes. Is it possible to save this plant at all?? I don't want to lose any more leaves.

Thank you!