I am not familiar with that orchid mix, so can't comment on it. Yes, the pot is too big, but has lots of holes for air, that helps. I would just cover the bottom of the pot with mix, put the plant in and fill with mix up to the the green part of the Phal. The plant would sit low in the pot, but you wouldn't have a full pot of medium that takes to long to dry, thereby inviting root rot. Don't water after potting, the soaked bark mix will be wet enough. I wouldn't fertilize until there is a sign of new root growth. When you do fertilize, use half the dosage recommended on the package.
I have two mini Phals. I'm babying, because of root rot. I experimented by putting them in Sphagnum moss and it resulted in root rot. Other growers have great success with moss, but it's not for me. My two little ones are back in bark and I'm hoping for a complete recovery.
I wish you luck and don't get discouraged if things don't change as fast as you expect.