As with almost anything else, the best way to learn is by having something real to do.
To pull an off-topic example — most people who are virgins can read all they want about s*x. But unless you start to try, and to get good at it (real thing to do) — you will never learn. And believe me, its something you need to learn to become good and be an expert. Haha.
Same thing with Phoenix & Elixir.
Unless you have a real project, you are going to really suffer. And your’e going to go nowhere.
Think of a project that you want to do that is pretty small. Start with that. You can learn Elixir syntax in a day, and the basics of the Phoenix Framework in another few days.
But you will not learn the patterns needed to write good software unless you have to write a real project.