PhD programs in the US and elsewhere are different: most PhD programs in the US are significantly longer, and could be seen as combined Master's and PhD programs, admitting students directly after their undergraduate degrees. The first year or two could be seen as more of a Master's program, and many programs give Master's degrees at some point in the process (some by request, such that the difference between having a Master's and not having one can be whether you decided to file a form or not). There can also be a certain filtering process at some point in the process, with some form of qualifying exams with three possible results of failing, being given a Master's degree but not being permitted to continue in the program, and continuing on to a PhD.

The result is that for many PhD programs, the first year or two transitions from being fully class-based (though often very small classes) to more and more research, and then finally a switch to having no classes, and only research (and teaching).