A Shy Hello From Singapore,

[silken]

Pictures of the roots would help. But generally if the roots are firm and either green(wet) or silvery white (dry) they are healthy. Soft mushy or hollow roots are dead and should be removed. You can cut up to a healthy portion if one is partially dead. I like clear pots for Phals because you can see the roots and when they are green, it is still wet in the pot and not time to water. When they look dryer (more silver white) they are dry and likely time to water them.