Phals grow in trees in tropical, humid but very warm climates, the bare roots clinging to the branches of trees or, sometimes, rocks. The roots get wet from the rain, dry quickly, and get wet again. The roots are completely exposed to the very humid air that moves gently past it.
When we use medium for orchids, this is to help keep the air around the roots humid and to keep the orchid steady in the pot.
There are many, many ways to grow Phals successfully. I like to easily see my roots so that I can tell when to water. When my roots turn from green to white, it is time to water.
I grow my Phals in 'net pots' that are just slightly larger than the root ball and use NZ sphagnum moss (AAA):
Example of the pots:
Net Pots | rePotme
Example of the Moss:
AAA New Zealand Sphagnum Moss
This allows air to get to the roots, preventing 'root rot':
Root rot - Wikipedia
When you take the orchid out of the pot and medium, remove all the medium, rinse the roots, then soak the roots for about an hour. If the roots stay brown and are not firm, they are dead. If any roots become firm (they will usually turn green but could remain white or be stained brown--firm is the key) these are good roots. Remove any roots that are dead. Let the good roots dry before 'potting' the orchid to help deter Phytophthora.
Good luck!