Phosphorous is an element without which Earth-based life can’t exist, and it is surprisingly rare. It can’t really be ‘manufactured” and there is no substitute for it. Supplies are not infinite.
There is a theory that the amount of surface phosphates available at any geologic time determines how much biomass (=life) Earth can support. This might explain why the Earth was apparently much more “lush” in the past than it is today, as evidenced by fossils.
Birds manufacture it...