There's no shortage of phosphorus. As prices go up extraction from human waste becomes profitable and all municipalities just do it. We invest in closed loop systems we stop having to think about energy and agricultural inputs as extractive, there is minimal possibility of "shortage" it's just a closed-loop system that occasionally needs to be topped off a bit.
You don't "just do" anything on that scale.
But you do them.
We have a shortage of refined Lithium and Phosphate. We have no shortage of the unrefined elements in profitable concentrations.