Wow, this could be a long and technical answer......Um, I'll try and keep it simple....maybe in 2 parts.
First maybe we should understand the relationship between soils and P. This will touch on Ca a very little bit. Then I'll go after the question more as you asked it.
Resupply of P in soils are dependent on a complex soil chemistry.
Many factor's effect the availability of the P to the plant. Amount of P applied by nutrient, soil pH, amount of Calcium (available) in the soil, temps and moisture content of the soil.
At high soil pH, most P is in the form of calcium compounds.
At low soil pH, most P is in the form of Iron and Aluminum compounds.
Maximum phosphorus availability occurs at a soil pH between 6.5 to 7.0. This is why one of the most important benefits of liming acid soils is improving phosphorus availability.
Now then. Yes they do interact between each other too. This can be rather complex.....I'll be as clear as I can be.
This is because they both support and counteract each other. They are up-taken and moved around the plant at the same time.
The "counteraction" is from precipitation of less soluble calcium phosphates at the vicinity of nutrient-absorbing roots.
Use of calcium can increase P uptake and too much P can block calcium uptake.....Fun eh?
Looking at the OP's pictures (or any "too much P situation). You can see that the high P is blocking Ca uptake, and you get those signs of low Calcium by the brown spotting on the yellowing leaves. This does not happen all the time here. The amount of P can be right at that blocking level and not quite be doing enough to have the Ca def expressed to that point of visible problem. It is still low....
This problem can be also linked to pH problems in the same way and a reverse of the P to low availability, comes into play here also.
This chart shows what I mean here pretty well for pH effecting availability. It is important to understand that when you water with your feed solution, that the soil pH drops..Somewhere
around a whole point. As this soil dries out. You get a rise in the pH back to the soils "resting point".
This is natures way of making everything available at good rates for the plant to use what it needs.
The relationship between Ca and P, and the effective uptake by the plant is why I like to say to pH in bloom to a cpl of tenths higher. 6.7 over 6.5 to use that Ca/P relationship to have them both available at the peak time of plant use (I know a well known breeder that pH's his organic feed solutions to 6.7 - even though he doesn't really need to (the soil self pH's thing). He wants to make sure his solutions are delivering his P in a proper relationship with Ca to have maximum availability to max his results.)
We all have our own way of doing things.
Again this will be effected by the amounts available....Too much P - to low a Ca and too much Ca - too low a P uptake.
On a side note. In synthetic use. Silica can cause a reaction with ca to form a precipitate. That lowers P availability too...
This is why you should be careful with any use of Si.
I should note here, that if in soil. The soil will supply the plants needed amount of Si and supplementing it is
not required...
For the most part, Si supplementing, even in hydro applications is not
required. It can be a fair idea to try adding it as it too, regulates P in the plant. That's a good thing - Again, used in moderation.
This what you were looking for?
I tried to keep it short and understandable.
