Phalaenopsis yellowing leaves and wilting flowers, possible rot

[anneVB]

My boyfriend's Phalaenopsis has yellowing leaves. the two under leaves (were completely yellow, no brown spots) fell off as soon as I gently lifted them (to try to see any further rot) and when they broke off, there was quite a bit of slime on the wound. The flowers (bloomed over two months ago) are wilting all at the same time (two already fell off) and there are visible issues with some of the exposed roots shriveling, as shown in the photo next to my finger). He says he waters it by filling the pot with water and then letting it drain in the sink. It has been in the coldest corner of the flat (he lives in a very small urban apartment) next to the window (blinds are usually down) but the temperature dropped here in Virginia Beach from the 60s to the low 40s last week, and has been staying cold outside. He works 9 hours a week, so he doesn't use is heater much, and it may have been as low as 64 degrees Fahrenheit in the apartment. Since the first two flowers fell off, he opened the blinds "so it could get more light," but I have a feeling it just got even colder without that additional barrier between the cold glass windows and the pot. Also, as you can see, the small very top leaf (that started to grow) turned black and has a dry white (possibly mold?) substance on the undersides.

I moved it away from the cold window and tried to water it a little a couple days ago, but it's just getting worse! What can I do to save this beautiful "White Wedding" Phalaenopsis??