I'm afraid I agree with everything above. This is too far gone. Once the leaf turns yellow at the base that leaf is going to drop and you pretty much can't stop it.
Adding a bag to keep in moisture is unlikely to help as it's already having problems from being too wet.
The small chance is if the roots are still good. (Might be worth taking a look at them). If there is a healthy set of roots in the pot then they may be able to grow a basel keiki. I know others here have succeeded with that. For a chance of that I would repot in a dryer medium and then try and care for it as you would a healthy phal (take a look at Philip's
The Phal abuse ends here sticky for general care advise).
However the chances of this are very very slim and the effort is probably not worth it. You will get far more enjoyment from a new one.