I get that. That's what I mean by seeing more content on the webpage. Assuming the page is a simple one, the amount of the webpage you can see on both 720p and 1080p would be the same. But if the page is more larger, complex, then you'll be able to see more on the 1080p screen, and on the 720p screen, you might need to scroll around. So my understanding is correct then.
Correct, you will see more, as there are more pixels to display the content.
However, what I wanted to do was point out that everything gets smaller, because your phone screen has not changed in size. (Assumption is comparing a 5-inch 720p to a 5-inch 1080p display.)
This might not matter for certain things, but it could also be the difference between something being readable, and too small to see.
Of course, once you doubletap to zoom in on the page, scaling takes effect, and it no longer matters, as both screens should scale to the same "size", in which case the 1080p display will be sharper, as it has a finer pixel array.