Hello

So i bought a phal that was on a sale, so maybe it was a bit neglected. Anyways, there's a few problems(?). The roots turn grey too quickly after watering. Some of the roots look yellow/rotting. The leaves are patchy and some of the edges are dark reddish. The bottom of the stem is also kinda dark red. Air roots are dried up, should i cut them? Also, should i take everything out and cut the yellow roots? If i do that, can i pot in the same medium?
ps. They're near a west window but not directly on sun
(I was going to upload pictures but i can't)