What can I do for rotted roots or What is "sphag and bag?"
Remove the plant from the potting material, and remove all the growing medium from the roots. Next comes what is commonly referred to as the sphag and bag method. Put styrofoam packing peanuts (make sure they are the real styro by putting water on them first) or LECA, or stones, or charcoal, or mixtures of the three in the bottom of the pot. This is to improve the drainage in the pot. I then soak high quality long fiber sphagnum moss (hereafter referred to as sphag.) in rooting hormone. The long fiber moss doesnt break down as quickly and plants root well in it. Apparently, there are natural fungicides in it...or something that inhibits fungus and encourages stressed plants to root. I trim the dead roots off the plant with a clean (sterilized) single-edged razor blade or an Exacto knife, pour Physan20 on the roots, then put cinnamon on the cut areas, and rooting hormone everywhere else on whatever roots are left. I then squeeze out the sphag until it is as damp as a well-squeezed sponge. I wrap the roots in the sphag, and place it in the pot, putting more sphag loosely around the roots. Make sure you dont smash it in, as it can be really hard to re-water, or may take forever to dry causing even more rot in your plant. You may need to put a bamboo stake in the pot to keep the plant upright in the sphagnum.
I then put the plant and pot in a plastic bag, but I leave the top open. This increases the humidity around the leaves and the roots, if there are any sticking out of the sphag...only usually I don't leave any aerial roots upin the air, but put them in the medium as I want the plant to maximize it's hydration. I don't close the top as I want some air circulation. This is up to what you choose to do. Some people close the bag, and use ziplock (or seal-able) bags. Someone here, and I am sorry, I forgot who, uses the veggie baggies which have little holes in it for air exchange. I have found that sometimes closing the bag is a recipe for disaster. Do not, however, let the leaves touch the plastic as that can encourage rot, not always, but I have had it happen. Blowing up the bag before sealing helps keep the bag sides away from the leaves.
I don't spray the plant, as I have had bad experiences doing so. I will, however, spray the top of the medium on occassion. Usually, the plant does just as well without it. I make sure that the plant is in bright, but not direct light (i.e. normal light as the roots and leaves if they are there do undergo photosynthesis), and that the temps are a tad warmer than usual--much like you would care for a seedling.
The most important thing to my mind is keeping the humidity up, as the plant has very little to replace moisture since the roots are impaired. I would never cut a leaf off a plant if it isn't yellowing. Phals do not have pseudo-bulbs so all food/moisture is stored in the roots/leaves. If you keep the ambient humidity up, the plant will pull from the air and less so from the...