Hi Denise. Welcome to OB.
Does the Phal. in question have any good live roots left? If so go ahead and repot it in fresh medium. Phals are really pretty hardy. I've pulled more than one back from almost certain death.
Cut off all of the rotted and dessicated roots with some sterile scissors or knife. Sprinkle with some regular old cinnamon, and then repot. Put it in a warm low light place and then wait. It could take quite awhile for the plant to start growing again, but I definately think this one is saveable. Good luck and keep us posted!