Toxicon is handy when you need to travel longer distances in a shorter amount of time. Instances where slidecasting might result in you getting clipped as a mechanic catches up to you. Phlegma isn’t meant to be used as a movement tool—its uses at an optimized level are calculated to fall within raid buffs. Not be saved for heavy movement. And this ain’t counting instances where you won’t be in range to use it anyways.

I’ve found plenty of uses for Toxicon, especially if I’m down Swiftcast because I used it on Egeiro versus for movement. The main issue is their generation being a DPS loss more often than not.