What is the material tied around the stake and the stem of the Phal? If it is the cord you are using on some of your Phals the cord could have gotten wet, created a bacteria on the stem and the results would be the same as crown rot except it started low. I see viable roots so don't think you have a root problem.

Crown rot and stem rot are the same thing except stem rot starts low and goes up the stem and crown rot travels down.

Brooke