Phal roots black

[CariC]

Hi everyone! I'm repotting a phal, and some of the roots have black places on them. Normally, I would think they were sick and cut them, but they're firm and plump roots that look otherwise healthy. I'd hate to cut off so many roots if they're okay, but I also don't want to lose my phal to a preventable disease.

I've attached a photo for you to see what I mean. The black doesn't show up really well in the image, but at least you can kind of see what I'm talking about. Thoughts?