Earlier quoted context omitted.
> the difference between masters and PhD has nothing to do with classes. huh ? what's your education system ? in europe it's generally 3 year bachelor, then 2 year masters, then 3 years phd so when you have classes during your phd hopefully they are different that the one you get during your masters
In the US, it's typically a 4 year undergrad, 2 year masters, and a ~5-7 year PhD depending on the program itself. From what I understand, while there are some classes you take as a PhD student, a majority of your work is doing research
For PhD students, the masters is integrated into the 5 years they spend doing their PhD. They are expected to take courses as a "pre-candidate" and do primarily research after they pass their qualifying exams and become candidates.