Homenewbie, First recommendation is do some research on where your Phalaenopsis orchid grows wild, and what the weather is like there. You, simply stated, are going to have to reproduce a climate that pretty closely resembles what your orchid would expect if it were growing in the wild. Not exactly, but fairly close. Your photos really help and verify some conclusions I made reading your initial post. One question you did not answer though, was where are you located? That is going to get to be important as we progress along.
You obviously purchased a nice well grown plant in full bloom. Your plant is obviously not in the best of health right now, but you may very well not be the sole culprit that created the plant's problems. The grocery store where you purchased the plant may have been diligently creating the problems long before you purchased the plant, so don't be kicking yourself around over something you may not be responsible for. Lets do some learning and see if we can fix what "ails your plant.
Most orchids grow in jungles usually attached to trees, or rock faces, but they are NOT parasites. Orchid roots grow among the roots of other plants, lichens, and mosses that you would expect to find growing on tree and rocks in the jungle. When it rains, the entire orchid plant gets soaked, and as soon as the rain stops, the orchid drips dry, and as time passes, the roots begin to dry also, and continue to dry until it rains again. Between rains, the plants, and roots absorb moisture from the naturally high jungle humidity, and at night from dew. The plants thrive on, no, they actually demand this soaking, drying process, and the drying is equally as important as the soaking.
Your orchid probably came potted in a clear slotted plastic pot similar to the one you used, but for shipping, they usually slip this plastic pot into a ceramic pot that has no drainage holes. The poor clerk at the grocery, having been told that the orchids were mysterious tropical plants figured he should keep them watered all the time, and proceeded to keep the outer sleeve(pot) at least partially full of water. A week of that and you have a blooming dead orchid sitting on the shelf. We call that root rot, and because the plant grows so slowly it usually takes a week or two for it to start showing signs of stress and death. First to go are the blooms, then the plant begins to become limp, and discolor, like it isn't getting enough water. So what does the inexperienced grower do? Why water it, of course!
Orchid roots growing out in the air have a dull silver look. Orchid roots growing covered with lichens, moss, and potting mix will have a translucent greenish yellow look. The stumps of roots that we see in your photographs are basically healthy roots, except at the very ends of what is left of them show the black mushy look of root rot. You were on the right track by cutting the rotted ends off the roots and dabbing it with alcohol. A better approach would have been to cut them off with a sterile razor, and set the plant on a shady shelf for a day or two to dry out before you repotted it.
My recommendation for recovering this plant will require some time, and patience. Patience is an absolute necessity when dealing with plants (especially sick orchids.)
I usually recommend a bread bag for this, but your plant is a bit large for most bread bags. Get a plastic bag that you can seal the opening on...either tying it, or zip locking it. Punch a few holes in the top of this bag...a hole punch, or a pencil size will do. take your plant out of the pot, and cut the bloom spike off leaving about a 1 inch stump and let it stay out of the pot and dry off for at least 24 hrs.
When you are ready to proceed, take a hand full size clump of Sphagnum Moss, or a hand full of your orchid mix wrapped in a scrap of cloth, wet this material thoroughly and place it in the bottom of your plastic bag. Take your orchid plant and place it in the bag roots down. It won't matter if the roots actually touch the wet material in the bag, but you don't want the roots covered by the wet material. What you are actually doing here is creating an atmosphere with high humidity. The orchid will pick up moisture from the air/slight contact with the wet material in the bag, and this will sustain it until it can put out new roots. Hang this bag in a bright room with no direct sunlight. If you are in a temperate location where the temps will not go below 60 degrees F. at night, you could hang it outside in a shady location. When I had a greenhouse, I would hang these bags under my benches. When the material in the bag starts looking a bit dry, take it out and re-wet it. Continue this process until your plant has regrown a new root system. If you have questions, post them here for answers.
You may get several replies to your original post here, and they may suggest different ways to treat your plant. Don't let that discourage you, there are many ways to grow orchids, and a lot depends on where you are located. If you read most suggestions you get on here carefully, they usually are really all very similar, and some techniques may work better for you in your home/geographical location than others, use what works best for you, None of us making suggestions here will get upset, all we want is for you to save this orchid, and one day step out of this "Newbie" classification you put your self in, and join us growers in a really fun hobby. Do some homework, either on line, or in a book, to find out what climate your Phalaenopsis Orchid would like, then expand to other types of orchids. You may actually find you have orchids growing in your yard. There are a few north of the Arctic Circle.
Q