McQuarrie's "Star Destroyer" redesign of the Enterprise was from the Planet of the Titans film project in late 1976-early 1977. When that fell through, Paramount, which had been vacillating between reviving Star Trek as a feature film or a TV movie, decided to bring it back as a weekly series to anchor the fourth network it was trying to create (the same thing it later did successfully with Voyager and UPN). That's the project that was called Phase II, and that was well into production as a TV series when Paramount decided to change it to a megabudget feature film to ride on Star Wars's coattails. Phase II went with the ship design that's been talked about in this thread, designed by Matt Jefferies, Joseph R. Jennings, and Mike Minor. Ralph McQuarrie was long gone by that point.
Although contrary to popular belief, the "Phase" part was quickly dropped and the series was known through most of its development as Star Trek II. These days we call it Phase II to avoid confusion with Star Trek II: The Wrath of Khan (even though that picture was originally released as simply Star Trek: The Wrath of Khan) -- the same way we refer to the original pilot by its working title "The Cage" rather than its production title "The Menagerie," in order to avoid confusion with the 2-parter of that name.
Although contrary to popular belief, the "Phase" part was quickly dropped and the series was known through most of its development as Star Trek II. These days we call it Phase II to avoid confusion with Star Trek II: The Wrath of Khan (even though that picture was originally released as simply Star Trek: The Wrath of Khan) -- the same way we refer to the original pilot by its working title "The Cage" rather than its production title "The Menagerie," in order to avoid confusion with the 2-parter of that name.
