Thanks for all of the feedback on this. Here's where I ended up:
Love the patch points for this!! So easy to set up parallel processing that I expect to use this feature a lot. This was super handy as the vocal in question was a blend of two mics and I could assign both tracks to send to the same patch point and each parallel processing track got the right blend of the two mics.
On 3 parallel tracks, I ran 1) a tape sim delay; 2) VoxTools with Cylon, Megaphone, & ADT at various levels; 3) TH3 with a Marshall-type setup. Each track blended in to taste.
I tried a phaser on another parallel track, but had an idea that ended up way better: I cloned the original tracks and then manually shifted their phase by 1/2 of a wavelength. I then automated pan and volume oscillations in time with the music (1/2 notes for pan & whole notes for volume). This gave a really neat effect as the the timbre of the vocal was changing in a really dynamic way and gave a bit of a swirling effect.
In the end, I didn't completely destroy the vocal, but blending that stuff in with the unprocessed tracks gave it a distant, ethereal effect that I ended up really happy with.
I love this forum!
Seth