droopy phal

[tetra411]

Hi all-
I've had this Phal for 5-6 years and it has been very hardy and easy to grow, and never before given me any difficulty. The last 6-8 months have been different. It has lost many of its bottom leaves and finally the leaves that it has left have become droopy and wrinkled. The roots that seem the healthiest are the ones that are aerial (and these are actually starting to turn brown part way down the root), although there are 1 or 2 in the bark mix that look good. The phal sits on a table on a northwest facing window in a steam radiator heated apartment (around 80 degrees all winter). I water it about every 7-10 days and fertilize with an orchid fertilizer (19-31-17) every other watering.

any advice would be much appreciated!
thanks!