I killed my first phal. It was so pretty, too!!
The same things happened to my phal- losing leaves, shriveling, and looking really sad. I bought another phal and the same thing happened! Argh!
All the roots had rotted off, and I learned that you need to pot phals in a chunky bark mix, in a VERY snug pot that hugs their roots, and have many many ventilation holes.
After that, I just water them once per week by sitting them in a slightly bigger pot.
Phals LOVE air around their roots.
For what it's worth, I am working on a phal that only had 2 roots and 3 leaves when I got it, and has now firmly attached itself to the pot that its in and is doing wonderfully about 8 months later. I don't have a flower spike from it yet, but I think it will bloom again in another 1-1.5 years.
Here is how I've potted my phals- you can make the holes in a water bottle yourself:
Sorry that the image is sideways, but I hope you see what I mean.
So yeah, this is my advice, but find what works for you because there is a lot of other great advice on this forum!