After some work and digging, it appears that it's not possible to get beyond 248 brewing on Phinny. Is this correct?
I believe that is correct. Kaladim Constitutional are 300+, but require soda, which is not in game until Luclin.
BTW, if your interest in Brewing is due to the Coldain Ring Quest, I have Mind Melts for 200pp. Send Buddi an in game e-mail if interested.
Yeah a lot of what can be made in many tradeskills can't be done because zones or items aren't in game (since technically they didn't go that high in such expansion).