I use phosphates for P. But I can tell you that by adding phosphites to my foliar regimen, I have cut my phos acid use (thru drip irrigation) by about 70% with better results. I don't think anyone here is suggesting the use of phosphites as a P source, but there is not doubt in my mind (and a large percentage of the farming industry) the use of Phosphites definitely enhances P within the plant. Any thing we can do to reduce the use of phos acid soil applications is a good thing. The side benefit of being a mild fungicide has been well known for many years.
I can tell you that foliar application of phosphites means near-nil P nutrition for the plant; it's a simple fact that phosphites mostly stay as phosphites inside the plant. What is most likely happening is you were previously over-applying P, which is very common amongst growers. And thus when you backed off on P, and didn't notice any negative results, you incorrectly attributed it to P that you thought you were getting from phosphites; but your plants aren't getting any more than near-nil P from phosphites if foliar applied.
Did you read any of my references yet? Also, if you foliar apply phosphites you are stopping AM fungi from infecting your plants...
When you attribute less need of phosphoric acid (phosphates) to your use of phosphites you are using a common logical fallacy called "Post Hoc Ergo Propter Hoc", in English that means "After this, therefore because of this." Basically that means you are assuming casualty incorrectly.
- "Post Hoc Ergo Propter Hoc": http://www.nizkor.org/features/fallacies/post-hoc.html