If the plant is healthy but the roots are rotted then it may be possible to save it.
Many people have done this with a technique called Sphag-n-bag. I can't find the links just now, you may find it searching this site or maybe someone else will know the link.
It sounds as though the yellow leaves may be like that because they have died due to lack of water rather than because they have rotted as such. Although I can't tell that for certain without a photo.
On the question of watering, I water by the same rules all year arround. I don't mean that I water the same amount all the time, but that I use the same indicators of when to water all year.
Do you have a clear pot on your Phal? That is the easiest way to know when to water. Wait till the roots are silvery in colour, then water by running water through the pot or by dunking the pot in water. Whichever way you water drain well afterwards. The roots will go green, while they remain green don't water again.
Another method is to put a wooden stick in the pot, right down to the bottom (without damaging the roots). Leave it there a few hours and then pull it out. If it is damp then don't water yet. I use this on by Dend with is not in a clear pot and I leave the stick in all the time and use the same hole each time so I know there are no roots in the way.
Another method, although it takes more practice and experience is to go by the weight of the pot. Feel the weight of the pot when you water, then again as it dries out. You can then learn to tell by the weight when it needs watering again. I think this method needs you to use one of the others first though while you learn what weight to expect.