I think many other people have posted good advice on how to get ready. I just want to second the other post that recommends against preparing for it. When you interviewed and got hired they knew your qualifications and knew you might not know some things. You're about to get paid to learn what they need you to learn. I don't really see why you should your own personal time learning something for them. Instead, I'd re…
You can learn a stack but still not have a great grasp of how MVC actually works and how the framework interacts with the database.
Instead of going over algorithms or frameworks, I would make sure you understand basic data structures and databases. You're going to be working with these no matter where you go.
For data structures, I would focus on hash maps and queues; you'll likely be using those much more than anything else. I would make sure to have a solid foundation in SQL queries because then you'll know what the framework's ORM is doing. Also you mentioned working on backend, so SQL should be your bread and butter (you need to know to avoid N+1 queries, etc).
I've gotten many interviews and at least one job based primarily (after being a nice person to work with, anyway) on having a good foundation in SQL; I wrote a toy ORM and put it on github.