Ok thanks for the input everyone! Actually, in the past couple of years, I had my phal seedlings (equestris, bastianii, amboinensis, schilleriana, stuartiana,etc.) in 65 deg temps with no issues, other than the fact that they grew more slowly.
The humidity is around 50%. Maybe it goes down to 40% during the drier seasons but never any lower. I have most of them in fir bark, a few in sphag.
But this year, I have some "weaker," more picky growers such as Phal tetraspis 'C1' and Phal violacea var. Indigo. I heard they get stunted and suffer for months if they get too cold.
Whoops I should've said "turn up the heat" not "turn on the heat." Of course, I do keep the heat turned on, just not very high.