Edited to properly reflect the issue. Turns out the plant was suffering more from being roasted than anything else.
Picked this poor thing up for a couple of bucks at Lowe's. The leaf damage is from sunburn, they'd put it out on the clearance rack in full Texas sun. The white parts feel like regular leaf, just dehydrated, so I'm waiting to see what happens before I cut those parts off.
It looks like the plant was growing really well in this pot before being brought to the store. Lots of nice long roots. My guess is the grower watered a lot less and the plant did fine until it got to the store and was soaked. Moss was breaking down, but the roots weren't as bad off as I thought. They were all green down to the tips, though some had patches where only the center strand was left. I didn't see anything that looks like a fungus to me, just some dead areas, so I took the risk of not cutting any of the big roots off. They seem to still be working.
The new pot is a bit larger than the old. Substrate is Better-Gro phalaenopsis mix with a bit of LFSM added in, which is working out well for my mini phals. Hopefully this one will like the mix as well. I haven't watered it today, I'm guessing the roots will benefit from a day or two to dry out.
Any tips? I'm planning to let it go a couple days without water, then just start treating it like a normal phal, albeit very slowly introducing it to light. It'll be in front of a South-facing window, but the window has UV blocking film on it, so it doesn't burn more sensitive plants. My other moths are doing fine in front of it.