I'm going through the first book right now ("Mastering Phoenix Framework") and I find the structure to be well paced for my taste. It skips the unnecessary details and goes into explaining general concepts very well.
I'm a bit turned off by the abundance of typos and code inconsistencies though.
Code snippets seem to be a mix of Phoenix 1.2 and 1.3 and some fragments make no sense.
For example, on chapter 4, it talks about adding categories to products and then, out of nowhere product.image shows up in the code snippet.
Of course, if you've been writing some Phoenix code before, these are easy to ignore and not as important. But they do add up and lower the overall quality of the book in my view.