People are 1% phosphorus”P” the average adult contains 700 mg (0.007 kg) of P.
To have another 1 billion(1000000000) people would require 7 million (7000000)kg of phosphorus.
What that is in phosphate rock I am unable to calculate but I suspect it is a large amount and yet people are beginning to talk about peak phosphorus. Will there be enough for 9 billion HEALTHY people?