Removal of mushy root in a phal

[Kalos]

I am new to this board, been lurking for a few weeks, this is my first post. I have a little Phal. Mini mark holm who has not done very well since I purchased him. I think it had a hard time transitioning from a greenhouse into my house. Anyway my specific question right now is this: There is one long root that is mostly green, plump, and appears healthy except for one section in the middle that is brown and mushy. Classic root rot from what I read; however I have also read somewhere that as long as the string part in the middle is ok you should leave it alone. The root distal to the mushy site continues to look very good so I am having a hard time justifying cutting off several inches of healthy-looking root because of one inch of rot. What is the correct answer?? Should I cut it off? If so, where on the root should it be cut? Thanks in advance!