helpmepls I am sorry to hear about your phal, it definately sounds like it is being over watered.
First things first, take a look at the roots, are they mushy and rotten? are there any viable (plump and green) roots left? If so cut all rotten roots treat the rest with cinnammon, H2O2 or listerine and repot in new media (preferably barks if you have a heavy watering hand) and leave it in a shady warm place until it hopefully recovers
When you say only the stem and roots are left it may be a case of crown rot, it happens when you let water sit in between the phal's leaves they go quickly, but there is little hope, try to treat the crown with H2O2 and again, leave in a warm shady place, and avoid watering daily.
You must understand that most of us started out with a phal that was overwatered
it happens, not that it makes it any less sad
Keep us posted