Complex values in an interferogram

Hi everyone:) I’m sorry if this is a really naive question. But I promise that I didn’t post it here without trying quite hard to understand it. But I just can’t wrap my head around it…

So each pixel in a complex SLC SAR-image is a phasor. The real part being the amplitude and the imaginary the phase. But when you form an interferogram I’m not really sure about the output. So you align them, cross-multiply them and what pops out is, to my understanding, the interferogram. By multiplying two complex numbers you actually do some kind of subtraction and get a relative phase difference. Commonly visualized as the fringes in an interferogram.

But does each pixel of an interferogram contain information about the phase difference and about the correlation? And are they both the result of the same cross-multiplication of two complex numbers?
And maybe as a last question, why is the correlation not actually measured and “only” estimated? I think this has to with the multilooking that is performed, but I’m not a really sure about that.

I’m sorry for the naive and general questions. I know the answers aren’t super easy and could require some math. But anything, general concepts or pointer to more resources would be super appreciated. I found the ESA TM-19 but yet didn’t read it, but it looks very promising.