Donna,
Growing Phals in sphagnum moss in the cooler months its always best to keep the root zone warm. So if your growing on a windowsill but have heat mats under your pots you should be ok. Just don't let the leaves touch the window panes which I'm sure you already know. The mats will keep the air in the immediate vicinity a few degrees higher than without it.
You shouldn't worry about growing under lights in the winter either. If anything I find its better as you can adjust the amount and duration of light that they'll receive. Always sunny and never have to worry if you get a prolonged spell of gloomy days.
I have most of my seedlings growing on mats and under lights myself. The temp there right now is 78 and goes down to around 68 at night give or take a degree. I find growing under lights my seedlings are almost always in constant growth which is a good thing!
Oh, and with cooler temps the growth of spikes will slow down. If you have anyway of giving those plants slightly higher temps they should speed up alittle. If you opt to put them under the T5's just keep an eye on them. The warmth could potentially cook them.
Judi