Only a problem for chemical agriculture
Most soils are very good at retaining phosphorus, nearly all of it is in insoluble form which doesn't leach out - but plants can't use it in that form, either. In healthy soil, microbes constantly release soluble phosphates - but when you disrupt the natural soil life by applying chemical fertilizers and pesticides, or by depleting the soil's organic matter, you can run short of available phosphate.
To correct this, chemical farmers add superphosphate - rock phosphate that's been treated with acid to convert it to soluble form. Organic farmers, however, can get all the phosphate needed by returning plant residues and animal manure to the soil.
It's just another reason why chemical agriculture is unsustainable.
