From my own personal experience, you do not need to learn OTP, processes, GenServers, etc to get started with Phoenix.

What’s nice is that Phoenix and Ecto both use OTP and processes under the hood. So you’re getting a good amount of concurrency and fault tolerance for free. For example, every HTTP request to Phoenix already spawns a process to handle that request.

A common mistake for beginners in Elixir is to use GenServers when plain Elixir will get the job done.

I’d argue after the chapters you’ve gone through you’re fine digging into phoenix and ecto. I’d however suggest not dropping the book. Even if things might go over your head right now there will come the place where having read about those things will become something you need.

Personally, I would read at least chapters 7-10, it’s not as hard at it might seem, and explains important concepts.

You could probably start writing Phoenix apps right aways with your current knowledge (plus asking your favorite LLM to explain certain aspects from time to time), but having the right understanding of fundamentals is very very useful in the long term.

You can also just skip the hard parts and continue reading; the things will get progressively easier once you revisit the book after some real experience with the language.