1.) Are the yellowed leaves on the lower most portion of the plant?

2.) Have you taken the plant out of it's pot to check the condition of the roots? If they are brown and mushy and/or smell bad, you've overwatered.

3.) Did you inspect carefully for mites(although, the way you describe the deep yellow color, it doesn't sound like mites)? I check for mites by holding a white piece of paper underneath several leaves while giving the leaves firm taps. If you have mites, they will fall onto the paper and move around.

It is natural for the oldest leaves of philos(lower) to yellow and fall off.

A deep yellow color in some Philos could be either over watering or underwatering. Plants need less water during the cold months of winter, than they do in the late spring and summer. They're not actively growing during the cold months, so they should not be fertilized now. I would definitely NOT fertilize my plant now- wait until you see active growth(Spring).

Hope that helps!

growhappy,
Thanks for the good advice. I pulled it out of its pot and the roots were all white and had filled most all of the pot and started to circle around. Only 2 of tiny feeder roots were brown, all the rest were firm and white. The leaves are yellowish throughout the plant not only on the bottom. I didn't see any mites (had a prob with them on my brugs last summer so know what to look for now lol!)
I went ahead and repotted into a little larger pot with really well draining soil, and watered with a little superthrive added. It actually looks a little better today and has a few new leaves started. I guess I will wait to fertilize but maybe sneak in a little epson salts when it warms up to 60s at night ;D
I wonder if the problem could be that some of the roots had grown out the bottom of the container (had to cut them off when I lifted the pot) and into the clay soil which has water only a few inches down? Seems not to drain well after the heavy rains we have had lately, and since the flooding we got from hurricane Rita. Thus I have most of my stuff in pots now ;(
~SJN