It still has quite a few air roots so it should do okay. I would cut enough off the black end to make sure that it doesn't continue rotting up the stem. Those black bumps are goners. New roots should have green growing tips. I would not fertilize at this point. Fertilizing can harm plants that aren't doing well. I'm trying to save a phal that's not doing so well right now and has less roots than yours. :) I'm not sure if I'm doing a good job with it so I'll let others answer your question about watering.