Phal suddenly yellow and dropping leaves

[solus]

I have absolutely no idea whats going on with my phal. Shes a few years old and has always been perky and correctly colored. In August I went on vacation and the house sitter managed to give the poor girl sunburn, so those spots are older and she has been fine since.

3 days ago I had tons of flowers and was perfectly colored. I tested that the medium was dry and watered with the fertilizer the store had recommended
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Fast forward 3 days and I walked into my spare room (the room with the best indirect sunlight all day) and this is what my poor baby looked like. The roots still look perky and properly colored, the pot is draining properly, the medium is still moist in the pot and dry on top as it should be after 3 days, but the crown and top leaves turned bright yellow and the flowers all wilted. 5 leaves fell off. The 4 that remain are soft and sort of mushy. The roots coming out of the top part of the crown seem to be shriveling and the top is turning yellow, but the under part of the crown (the part under the medium) is still healthy and green, as are the roots coming from that part of the crown. What confuses me is that from the little bit I know these are signs of both too much and too little light, too much and too little water.

I could use any help I can get. Please help me save my little one!