You don't say how you are growing your plant but I'm going to assume its indoors/windowsill:

I think you answered your own question. Nothing to retain moisture (i.e. sphag), misting only once a day (and by what you're saying I'm assuming you don't soak it occasionally), and now its dehydrated. Its not getting nearly enough water! Phals really love their moisture, and unless you're in a greenhouse you'll most likely have a difficult time maintaining a mounted phal since indoors tends to be too dry.

If you're dead set on trying this plant (Can't learn if you don't try!), three suggestions to increase you're odds of success:
1. The LEAST you can do to help your plant is to put moss around the roots on the mount.
2. Soak it maybe every other day or so. Summer every day if not twice a day. Drop it in a bucket of water for 10 mins to get it nice and saturated.
3. If you have a well lit area, someplace like a bathroom or above your kitchen sink that gets good humidity at least for a small part of the day.

If its a mounted plant you want, and aren't set on using this phal, there are orchids more amenable to indoor mounted culture. People here have a lot of recommendations for you.

Good luck!

Thanks!

Drop it in a bucket of water for 10 mins to get it nice and saturated.

Does "drop it in a bucket" mean the entire plant, including the leaves? As long as the plant is mounted so that the crown points downward, will it be ok and prevent root rot?

Thanks!
Carol