Skipster, you are correct. The P may be tied up on microbes with no biology in place to cycle it.
This is a complex question. I'll do what I can to be brief.
The answer depends who you speak to. For me, any
mineralization is very dependent upon plant exudates. Plants will put compounds into the soil through their roots (proteins, carbs, sugars) in order to feed the biology which is responsible for mineralizing specific nutrients at the right place at the right time. I really like the fundamentals of this paper
There's a difference between inorganic (absorbed) and organic (microbial) P. The conversion of organic P to H2PO4
is a biological process.
Inorganic P is leachable and is quantified by soil tests
Organic P is not leachable and is also not (normally) quantified by soil tests.
Organic P is only available when the microbes die or are consumed by other microbes or arthropods through the biological nutrient cycle.
This is why (rightfully so) regulations are in place to restrict P. We have (in some areas) enormous leachable loads of P in soils but little biology to sequester (hold onto) it so it's available to plants when they ask for it. We've also done a great job at destroying the biology that will cycle P when it's needed by plants.
The problems lie at both the sequestration and cycling ends. We've done a good job at screwing up what took many millions of years to evolve.
Victorsaur, IMHO, mycorrhizae would be very useful to cycle P that's in place, however without organic matter you'll have anaerobic compaction which will NOT support a mycorrhizal system. It would be easy to tell you to buy mycorrhizae from us and make a few bucks, but it will not work very well without the right habitat in place. The diversity of a mycorrhizal system would not be supported with conditions you've described above, at least for not very long.
I hope this helps!