German visa for PhD candidate

To enter Germany as a Ph.D. candidate you need a proper visa. If you also have a work contract, you need a visa that allows work.
Such visa can be applied for at a German embassy. Contact your nearest one to ask about requirements and formalities.

Being a PhD candidate means studying for which one needs the proper educational requirements. If you fullfill them, then you get a study visa. Working is another thing. How can you take a job for a PhD if you are only a candidate and not a PhD? Having a PhD is one of the exceptions for which non-EU citizens can usually get a work visa but being a "candidate" doesn't mean much. It might show intention but not meet the qualifications. It's like expecting one can already drive a car because one has signed up for the driving school.

Thank you for your contribution to the thread. You may know that PhD is of two types in Germany. One is a student fellowship and the other is "mitarbeiter" which is usually 50 65 75 or 100%. I have got that kind of position and my friends are already doing PhD of this kind in Germany and they are there on work visa not a student visa. I hope that clears the situation.