If it is in a clear pot, it will be easy to see the roots. If not you need to be able to see the roots so a partial removal from the pot will be necessary. Posting a picture would be most helpful for those of us trying to help you. The most common mistakes with Phals are overwatering or underwatering. Most people overwater and then the roots and planting medium rot. I, on the other hand, used to kill them by not watering enough. I like to be different.
The roots should have some green color if it is getting enough water. If it is not, they will appear white, gray or beige. The leaves should be thick glossy and plump. If they are shriveled, there is a problem alright. Does the planting medium look like bark, coconut husk, or something else? Moss is sometimes used and it holds moisture very well. Rot occurs if watered more than it needs. I have phals planted in all those things and water the moss more carefully because of that. I still sometimes underwater because I am so afraid of rot!
My poor phals.
I have blathered on long enough. Hope this helps you. Carol