Books had a pocket glued onto the fly page. The pocket contained a card with the book name on it. When you borrowed the book, the librarian removed the card and wrote your membership number on it, and retained the card. The “return by” date was stamped on the pocket.
The book you were checking out had a little pocket glued to the inside of the cover that held a card with the book name on it. The librarian would write your number on the card and placed it in their filing system. They would then write or stamp the due date on the pocket of the card.
iPhone XR - I see no reason to upgrade as I have found myself slowly using it less and less for anything other than messages, maps, photos, and slack. Every once in a while I will install something and use it for a few minutes, completely forget its on there for a month, then delete it.