I don’t have the book store tab on the books app.

Since updating to iOS 12 and to 12.1.1, I haven’t been able to purchase books on my iPhone XS. I am able to do it on my iPad mini 4, and then download it on my iPhone but I don’t always have my iPad with me when I’m done reading a book. I can only access reading now, library, and search. I have tried searching in the store but nothing shows up. I looked at all my restrictions and I don’t actually have any restrictions set. I’ve tried deleting and reinstalling, signing out and back in with my Apple ID. Here’s a picture of the bottom of the screen in Books.