It is not so much a temperature drop at night. It is more of a seasonal drop in temperature. I think I've read a drop of 10 degrees F is sufficient. If you go from a hot summer to a merely warm winter, that could be enough.
If you are still not getting spikes, I would see if your light levels are adequate (if Phal leaves are perpetually very dark green, you might want to increase light a little, but do so gradually).