I think your real question should be what got me to this point. Saving the plant won't accomplish much unless you figure out what the problem is with your conditions. Good culture usually equals good plants.
Phals like it warm. Shoot for minimum 60F. They can take cooler temps but let's shoot for 60F.
The roots need moisture but also need to breathe, that's why they do so well when mounted. In a pot a chunky mix is best so air can circulate through the mix.
Humidity is good(they are tropical plants)60-80% RH is optimal but they will do fine at lower RH.
They need air flow. The plant can't transpire unless there is movement in the air.
As far as saving the plant with no roots, you can try a dose of seaweed extract, Kelpmax, or some other kind of rooting hormone on the base of the plant and keep it moist and warm. You might get lucky.
I don't think there's a foolproof method. Otherwise we wouldn't have a forum with 7,000+ entries about "How do I save my rootless plant"
Bill