The Cation exchange in a soil test is also a factor in the availability of phosphorus being able to be absorbed by and local plants.
In Illinois, Commercial applicators are banned from applying any phosphorus unless a soil sample shows the soil to be deficient. Then an applicator is legal to apply.
Even if you apply a 12-12-12 fertilizer, only a fraction of the phosphorus will be available for plants to uptake.
If only 25% of the P is available, the other 75% then creates P loading in the environment. If it's a synthetic source, then everyone wants to put a stop to it.
If you want results, just apply natural Urea, along with iron and call it a day.