Those roots look OK to me. One of mine has had a couple like that since I bought it about 8 months ago and they have just stayed the same and not caused a problem.
To me they look more like old dead roots than rotten ones, and the old roots do just die off sometimes and slowly become hollow.
Having said that, I'm peering at the roots of mine through the clear pot every time I water, to check they are not causing a spreading rot problem.
If you decide to re-pot you can check the roots then. If they are hollow and just have a brownish outer skin (with a thin 'thread' down the center), then they are likely to just be old roots which have died off.
If there is then still firm section below them I would suggest leaving them, the thin thread is the actual root and the surrounding material collects water and holds it next to the root. If a lower section still has this (can't remember the name of it) then it can still transmit water up the root to the plant.
If the roots are yellow/brown but firm then they are still good roots. Two of those you have indicated look like they may be like that. The green roots are photosynthasing and usually the yellow/brown healthy roots are further into the pot where there is no light. But mine has roots that look yellower/browner at the outside but still seem healthy. Maybe they have just stopped photosynthasising for some reason.
BUT if the roots are mushy feeling then they are rotting. Get rid of these as quickly as possible.
Basically, I have a phal which has been VERY healthy for the last 8 months (four new leaves in that time and a new flower stalk with about 16 fully open flowers at this momment in time), and the roots of this Phal look very similar to yours, right down to the odd dark almost black spots on the roots. I have kept careful eye that the dark areas are not spreading (whcih they havn't) and the plant seems to have thrived.
If you don't re-pot then I would checking the roots each time you water, but I don't think you have anything to worry about.