Lots of good advice here, Lisa. As to which roots to trim, any that are dried, or feel mushy should go. If you squeeze them gently with your fingers and they feel firm, I'd leave them. They are holding water.
One thing I'd add - when you're re-potting since you have had a case of crown rot on that first plant: when you're finished trimming and have removed all the moss from amongst the roots, gently wash them under the tap in warm water and while they are still wet, sprinkle cinnamon all over the roots. It is an organic fungicide and also somewhat antiseptic as well. So it will help your plants resist infection if there are still any fungal pathogens hanging around.
Yep, all my Phals are either mounted with leaves hanging down (as they grow in nature) or sitting in their pots on a slant. This way, water can't sit in the crown of the plant. The flowers are meant to cascade gracefully downwards, too, not stand up as they are sold in the stores. I think they pot them that way also because they can ship more plants in a box if the flower stems are vertical.
