My guess is root rot. I too would cut off the spike... [moment of silence], and repot it in something that dries out 60-70% in 7-10 days, whatever medium will do that in your growing environment. If there are less than 3 roots at least 3-4 inches long, I would sphag 'n' bag. That's my 2 cents.

Good luck to you! And regardless I'm happy you have been able to enjoy blooms for the past year, with all due respect to your phal's health.
