The manual is also available as an 843-page ebook [2], and is accessible via the Tips app, which is preinstalled on the home screen.
It's not quite like the days when a paper manual would be right in the box, but it's close. And I think most people would be unhappy if their sleek new phone came with an 843-page tome (not to mention how much paper that would waste).
[1] https://support.apple.com/en-gb/guide/iphone/welcome/ios