Too much water.
The media may be sour. Phals should be repotted every 1-2 years. Bark breaks down and becomes soft and rots. The media becomes acidic.
The roots are still green if they are firm, then the orchid needs to be repotted. I replied to your other post, so the method is the same.
Phals and most orchids need to be potted in a pot that just barely accommodates the root mass. All dead roots should be cut off with a sanitized knife or utility blade. Most orchidists will use a small torch to heat a pruner to kill pathogens and virus.
Always use a new pot and new media. Make sure the pot has a lot of holes in it . Make more if you have to.
Bark is the most common media, but I don't like it, I don't know how to use it well and I am not good about repotting. Basket culture with no media requires more water but there is virtually no chance of the media souring. the orchid will eventually grab on to the pot, you just have to make sure in the beginnimg it is secured so it cannot move so the new roots can get a chance to become established.
Baskets come in wood and plastic. Plastic is light, but a good wood basket can last over 10 years. I also like to use clay pots instead of plastic since they breathe better.
I will often turn a clay thumb pot or 2 inch pot upside down in a basket and secure the orchid to the bottom of the clay pot and then put the pot in the wood or plastic basket and hang it in a tree or on a fence. The pot allows air to circulate to the bottom of the plant and helps to keep the roots dry.
https://www.jimssupplies.com/store/index ... t_list&c=2
I water too much so I prefer basket culture that allows the roots to cling to the basket and hang out in the air. I have a lot less problems with root rot, but the orchid needs to be watered more frequently. Phal roots turn green or greener when watered and lighten or become white when it is time to water again.
Happy gardening in Hawaii. Gardens are where people grow.