I fermented feed for two years... if your flock is healthy already, it's a bunch of hype.
The nutrition experts who came up with the formulations for our feeds are well aware of this phytic acid issue and the feed is formulated to account for it.
So phytic acid and what... acid from citrus block calcium... but all these peeps acidifying their feed by fermenting (no it doesn't mold UNLESS you let the yeast run out of feed for themselves, then it does) and/ or adding acv to their water doesn't cause calcium absorption issues??
I live in the PNW... my OS gets wet... it's no big deal.