These days deploying elixir to pretty much any platform is insanely easy. Heroku, Fly.io, etc all have good guides for phoenix apps if that's your preference. Likewise Elixir's build tool Mix (Rake or NPM for Elixir) will generate a Dockerfile for your phoenix web application if you prefer containerisation. If you want to deploy straight onto a VM then `mix release` will setup the files needed to make an erlang/beam "release" with BEAM bundled in so you can run it without any special dependencies.
Looking at the contents of the book it looks like it goes into depth on how "releases" work, and gives guides to using a bunch of popular platforms like heroku, digital ocean, etc. It's looks like a conveniant collection of recipes for different hosting options.