This. If every class had its own spells I would advocate for the spells to be described in each class' pages; but as there's some overlap, it leads to having a ton of pages with spells and simply sorting them alphabetically makes this very annoying. Having them double sorted would definitely makes it easier on the page flip.In class would be better.
Also, spell descriptions should be separated by level, then every level by alphabet. So when we are looking for 1st level spells we do not need to search through 100+pages for 5 or so spells.