Vicki, I would trim the roots just above the mushy, rotted part, or where the velamin covering is broken. Unless you suspect a problem with this plant, or just want to be extra cautious, you don't need to soak roots in anything but water, mostly to help loosen old potting material. If you do want to take precautions with your phal roots, I would recommend Hydrogen Peroxide at the over-the-counter strength of 3%. Just soak a few minutes untill it no longer fizzes. If you don't see any fizzing anywhere, you are good to go!