There are other sources for phosphorous
There are plenty of other sources for phosphorous. The most obvious one is our waste. After all, the phosphorous that plants use just gets recycled into the ground or goes into our diet. Almost all of it that we eat comes out in our urine and fecal matter. So much of it can be recycled. We just don't do it today because phosphorous is still a lot cheaper from other sources.
Natural gas is very abundant outside of the US. It's believed China's supply of natural gas is greater than the US's. Britain has a natural gas field in its northeast that's as big as the Marcellus shale field in the US. It's thought that Siberia has huge reserves of natural gas. And so on.
Don't worry about biofuel using more NPK. It's just not efficient to make and use for plenty of other reasons.
