Your winter temps are not so cold for phals. I am not a big one on heating in the winter myself...haha, if you call what we have winter, but it does get cold to us Floridians
...I keep my home set at 62 during the day 68 from 5-10 (oh, not to mention thick sweats
) my home is warm 5 hours out of a day. Have 5 phals blooming right now that have come through my "winters". I would not worry much about the winters, if you feel it is getting a bit colder than you would like it, most likely your phals are feeling the same, move them a few feet away from the glass pane "bay window" should do well for you.