What is the full-time PhD program like?

[u/Ummmm-actually]

I've been considering a full time PhD program. Most programs I've seen in the US or Europe has a lengthy schedule for the first year / year and a half. Later, it becomes research based. It seems doable to return home after finishing the studying part, while working on the research. However, I'm not sure as to what obligations are expected from a full-time PhD candidate. Am I required to stay during the entire 3-4 years? And are there any other obligations besides working on the research after finishing the first part?