See annotations with the build-phases tag.

Why are the build phases not enumerated in the Nix manual? If the instructions on how to create a derivation (and thus, a package) then why not go all in instead of spreading out information in different manuals, making the subject harder to grasp?...

(By the way, it is documented in the Nixpkgs manual under 6.5 Phases; not sure why it is not called build phases when every page refers to them like that.)