Not the biggest problem
The "Green Revolution's food machine" is not sustainable in any case, the depletion of cheap phosphate is the least of its problems. Big ag uses it very wastefully, which has led to phosphate becoming a major water pollutant.
We need to stop wasting animal manure, in the first place. The use of cover crops to take up soluble nutrients so they don't leach away is also of great value - buckwheat is especially good at capturing P and making it available to subsequent crops. The use of fungal inoculants to increase the conversion of P to forms available to plants is also proving very valuable - most soils naturally contain plenty of P, but in the wrong chemical compounds.
