Repotted blooming Phal due to tiny white pests and withering roots

[swhite73]

I'm pretty new to orchid growing, and my latest acquisition has me running to OB every week! After "eavesdropping" for the past few months, I finally joined the forum today to make sure I don't lose another plant. Thanks to everyone for the great info and positive atmosphere!
I purchased a "just add ice" Phal from wal-mart in April this year. It's in an East-facing window behind blinds, I water every 7-10 days until the medium is moist but with no standing water. Room temperature stays between 74-80 F.
About a month ago the leaves nearest the window got patches that are white and thin with black edges - I took it to be sunburn as the patches are at the same level of where one of the blinds is missing. I fixed the blinds and the spots have stayed the same size and dry.
Then the top-most leaf began to curl under and started growing upside down. I redirected it to grow right-side up but it's still significantly curled. Since then a new leaf has grown and is now 1.5" long.
2 days ago I noticed white bugs crawling on the soil only. They're so small I couldn't tell whether they're springtails or fungus gnats. They don't seem to jump and I've had a few flying pests in my apartment too, so I'm leaning toward gnats.
When I examined the roots, all that are growing to the outside of the container appear to be healthy with several new sprouts forming, but roots in the center of the container are withered and brown and the potting medium seems very degraded. I have 8 beautiful flowers that I hate to lose, but I'd hate to lose the whole plant even more so I re-potted in "Hoffman's special orchid mix", which I boiled and let cool prior to potting. It has quite a bit of charcoal so I hope it will last longer than the medium my Phal came in.
Any suggestions, tips, or chiding? I welcome it all and will post pictures soon.

Thanks!

Sarah