PhDs are apprenticeships. Students perform original research under the supervision of a doctoral advisor, and submit their work to a "guild" of external reviewers (peer reviewed journals or conferences). Once the student has three peer-reviewed publications, they graduate.
"Once the student has three peer-reviewed publications, they graduate."
That's not a standard at all. You usually can't graduate without at least one peer-reviewed publication, but beyond that, as far as number of publications goes, it varies a lot from institution to institution. The biggest standard is that you complete a dissertation and defend it.
