I have contacted a professor (in Germany) to ask if he would take me as a PhD student.
I have written to him a follow up email 7 days after the first contact, and now it's two weeks with no answer.
Is it appropriate or advised to make a phone call to the administrative office of the chair, and understand whether the professor is out of office due to e.g. holiday?
This way I would know if and when to try the third email.