Right, thanks, now I understand. If you look at the screen, you will see that is within the box "Word count options", hence why there is nothing to do with page count in it.
Above it is the box for "Page count options". Any of the algorithms in the page count options box will give you the equivalent of a total page count, they just have differing ways of doing it. I suggest leaving it at the default of "Paragraphs (APNX Accurate)". Contrary to your apparent confusion, this algorithm does give you a page count, but it does so by trying to identifying paragraphs within the book as part of a way of estimating how many pages there are. That is why it says "Paragraphs". The other option in there of "Calibre Viewer" gives you the same count that opening the book in Calibre's ebook viewer, which is based on dividing the number of characters in the book into 1024 per page, supposedly some Adobe standard.