Digital booklet of views.

I'm assuming that you are trying to do it directly on your phone as you don't say otherwise, if that is the case then you need to use your computer's iTunes to download it and then sync it to the phone or use iCloud Drive to copy it to it : View iTunes Digital Booklets on your computer or your iPhone, iPad, or iPod touch - Apple Support

To sync it to your phone if not using iCloud Drive for Books, you need to download it on your computer's iTunes and then :

- if using a PC change its Media Kind to Books so that it goes it into the PDFs section of the Books part of your library

- if using a Mac find it in Finder and add it to the iBooks app on the Mac

It should then show on the phone's Books tabs of selecting and syncing to its iBooks app