Brown rice confuses me. On the one hand, may sources say to do what I did with the millet, which is a 7-hour soak in warm water with 2 tbsp of something acidic.
On the other hand, the best method is supposed to be the one where you reserve a portion of the soaking liquid each time, and use it for soaking the next time. After several iterations, the phytates are nearly gone.
The original source is here. The comments section had very useful information.
The blog source quoting it is here.
Here is a slightly different method that involves using a quart of reserved water, and whey. It sounds like a hassle, but the author describes the difference in taste in the brown rice, which to me is one reason to make it worth trying.
According to the comments section of the first link, whey doesn’t contain any phytase, so it’s not directly responsible for breaking down the phytates. But the acidic medium does help.
Finally, here is info on germinating and sprouting brown rice.