I don’t know in practical terms how Apple does it, I only know that they must do it because otherwise they couldn’t produce an artifact as complex as the iPhone. You can know for a fact they utilize modularity by opening up an iPhone and seeing… modules! A few things to read in the general area of this theory though…
An actual book that’s a bit broader but touches on system coupling/decoupling and is very practical for software people: Wiring the Winning Organization by Gene Kim
An excellent, very approachable primer on the overarching field of thought, which is systems theory, is Donella Meadows’ “Thinking in Systems”
Going back to more of the philosophical foundation (along with other valuable business ethics lessons), you should look into the work of W Edwards Deming and his “System of Profound Knowledge” — sounds pretentious but is EXTREMELY practical. This region of thought forms the basis of e.g. the Toyota Production System
And an absolutely excellent but more academic deep dive into precisely this topic of modularity is Carliss Baldwin’s “Design Rules.” It’s sort of a super-theory of Conway’s Law, but in a book-length argument.
