welcome Henk, I'm another newbie here. I've been growing phals for only 2 years, been pretty lucky so far, but I'm no expert . Like MarciaP said, the shop keeper was probable not very clear about the instruction on where to cut back the spike. You want to cut the "flower spike" only, cut it back to the node before the one the first flower bloomed on. Leave about enough space so the top of the node isn't bothered by the scissors, and make sure the scissors are sanitized.
But if you want your plant to rest, you can cut the spike all the way back near the plant itself,this way it's next spike will yield bigger and more flowers, that is, with all other essentials like fertilizer,humidity,air movement provided for . I'm sure some of the experts will guide you through.
