Professors are nice, no difficult question. Prepare the general common questions and a little bit of your major project . Two professors from unveristy and one from your major. Dont over thinking the process.

The PhD interview was conducted online. It was informal discussion with professors and current students. Current PhD students are passionate about giving you information about Stanford and department. Professors will try to convince you that Stanford is the best place for you to go and impress you with their research (because they are truly impressive!)