in your case I would probably cut below first flower. There is no guarantee it will develop spike from nodes left below any time soon. Plant will need to go throw period of cooler temps to get it bloom.
Also you have to keep in mind growers control temp to make them bloom at the time they want to sell it to you any time in flowers. usually phals start to bloom late winter - early spring.
there are debates to cut it completely or not. Some say leave it on some say cut. I noticed in my phals when I cut old spike they produced new one same size and amout of flowers. on ones I left spike on it did produced new spike from node but it was shorter with only few flowers on it.