I use mM concentrations of tetraethylammonium bromide (TEAB) as an amine modifier to my mobile phase. What can I use to remove this from my Zorbax C8 column? (I typically run at 100% ACN)

I read somewhere that a 50/50 mix of 200mM phosphate buffer and MeOH will work...but I'm a little hesitant to use a buffer. Will a 50/50 MeOH : H2O work?

Why do you hesitate?
First check up whether it crystalizes in such proportions or not (200mM is quite strong buffer), and go on!
I use to work A LOT with the phosphate buffers. Just have to remember about washing the external (pump's) piston parts (if your pumps has no such option) with water or mobile phase quite often, in order to prevent crystalizing outside.
I always washed my columns after working with phosphates with water/MeOH mixtures (or sometimes even with pure water, which was perhaps not very clever but at least made me sure there is no buffer inside).

Greets,
Maciej Turowski
KIT