Thx crazyhorse for the concern and the link, I am very aware of the dangers involved with reducing --> concentrating effect.
Therefore I suggested it only for making a 1 pull cold soak tea at ph4 (thus with no several pulls and no reduction phase). This way you can't even taste it. This I find the best point of phosA, the fact that you need only one (at max 2) drop, non-tasty, and still being a good agent for the alkaloids to come out and play.
For aya, I think I'm not going to use it anymore, too much water needs more PhosA, and extremely reduction. Things might differ if one neutralizes with baking soda, but the thick dark brown slurry after reduction is not friendly for the pH paper colors to check properly.
Neutralizing before reduction is perhaps more practically therefore, but the pH get really rolling during/after reduction, so it's less precise to correct before reduction. Best to save yourselves all the hassle and avoid phosA all together for all practices that involve reducing. Just my thoughts.
I did once neutralize with baking soda on reduced leaves tea, worked like a charm for pH sake but the tea got flocked all over, not a big deal if you shake well, but looked rather unappealing too, I know it's no gourmet contest.