Dark and shriveled spots on Phal roots

[CityGarden]

I've had this plant for over a year, and it was doing well until recently, when I noticed some dark spots on the arial roots. I un-potted it and found more spots on the roots- especially towards the ends. It also has a new leaf growing that seems to have a spot. The older leaves look OK. It lives in a clay pot, and I water it about once a week.

Any advice about how to treat this would be appreciated, pictures attached.

Thanks!