You should either cut or not cut. Cutting is better for the long-term health of the plant. Not cutting can allow the spike to branch and produce a few more flowers.

The reason that your plants have not re-bloomed is that the light level where you are growing it is too low. A nice east window without direct sunlight will do it.

The 50-60F instruction refers to the fact that these hybrids also respond to a fall temperature drop. I have heard of people putting Phals in the garage each night for a month to fool the plant.

Richards right, increase your light. I will say though that since you are in z6 they can take a bit of direct sunlight. Sun up till noon or maybe 4 til sunset. This is how I grow mine here in z7 and they thrive.