As far as I know, oat powder is ground oats, so it should have the same amount of phytic acid per gram as oat flakes, which is listed there at 1174mg per 100g.
At least a month ago, @Rob asked if there were any known problems with phytic acid outside of absorption issues with some micronutrients. No one had any information on that.
Chris Kresser references an article by the Weston A. Price Foundation that lists a few more issues.
Phytic acid not only grabs on to or chelates important minerals, but also inhibits enzymes that we need to digest our food, including pepsin,1 needed for the breakdown of proteins in the stomach, and amylase,2 needed for the breakdown of starch into sugar. Trypsin, needed for protein digestion in the small intestine, is also inhibited by phytates.3
It’s still a matter of the amount. Maybe reading some of the studies cited in that article will give us some useful numbers, but the 150 to 400 mg per day they recommend is probably good.
For me, the phytic acid problem is another reason to avoid a high carb mix.