It could be that my math is terrible, but it appears to me that these two traits do not stack. By default, when I have the staff out, Phase Retreat has a 10s cooldown. When I apply Illusionist’s Celerity, it drops down to 8s. I would think that with Chaotic dampening, it would drop a further 20% down to 6.4s or whatever the system rounds to, but it does not.
Because it doesn’t say it doesn’t stack, and of course it doesn’t say it does, I’m a bit confused and wanted to get the opinion of other people before I try and submit a bug ticket for something that is possibly working as intended.