Erosion of top soil is a more significant problem than fertilizer. With respect to fertilizers and inorganic phosphate supply, it seems that these are not really necessary(they might actually be detrimental) as long as you provide the right soil microbiome for the crops which can outperform synthetic fertilization[1-2] (though I am very new to this and is outside my field and I am unsure of the validity of their claims).

[1] https://www.youtube.com/watch?v=cO2nGHq40Xc [2] https://www.youtube.com/watch?v=ErMHR6Mc4Bk

The problem at the moment with renewables is they still don't provide reliable base load, and energy storage systems while useful locally are proving incredibly expensive at scale. The fact is the only option we have right now in many countries for reliable base load generation outside fossil fuels is nuclear. Some other options may eventually become viable, like geothermal or fusion, but there's no realistic prospect of that over the next few decades.

If we want to get serious right now about eliminating fossil fuels, the fact is the answer is a mix of renewables and nuclear.