Sorry to disagree, but I could've sworn that calcium phosphates (there's three common calcium phosphates), were insoluble. Meaning they would also need to be digested by bacteria before assimilation into plant roots. Plus, calcium compounds can't neutralize soil if their anion (the negatively charged part such as carbonate, hydroxide, phosphate, sulfide, sulphate, chlorides, iodides, etc...) doesn't easily absorb free acidic protons. Calcium carbonate would indeed be a Ph raiser because once it absorbs 2 acidic protons, the resulting carbonic acid (the carbonate anion that absorbed two protons), would decompose into water and carbon dioxide. This would mean that those two hydrogen ions were removed from the soil, raising the Ph. But a different ion, such as sulfate, would absorb those same ions, but also release them back easily because sulfate is highly soluble. This would keep the Ph fairly constant because no protons are removed during this process. The calcium hydroxide would be another ph raising salt because the hydroxide would absorb 2 hydrogen ions, and turn into water and calcium ions. That is why only carbonates of calcium (lyme) are usually used to raise Ph.
I have no problem with disagreement. In fact, there is much disagreement about soil science in general, with the spectrum running from manufacturers at one end and organic gardeners at the opposite.
Now that formal education is 50 years behind me, I finally regret not taking any chemistry classes. My article was based on lots of research over the last year and not personal knowledge. Unfortunately I cannot access my notes to respond properly as my computer died and I'm at the library using one of their computers. At some point I will have another computer and then I'll check my notes and get back to you. (I DO make regular back-ups so I have the data, just no computer.)
I randomly checked my textbook, and yes, phosphates are generally insoluble, but that doesn't mean plants still can't absorb them through their roots. In fact, phosphate salts might have the ability to increase mineral bioavailability by pulling the mineral with it as it's absorbed into the roots. But it's just an educated guess.
Thanks for checking. My understanding is that the microbial activity is what changes the chemical makeup so that plants can absorb more of the needed nutrients via their roots. It will be interesting to see what we learn over the next few years.