Leave Industry for Ph.D. without Burning Bridges
Be sure to consult your employment contract.

The professional thing to do is to give two weeks notice.  It is your manager's job to be prepared for the departure of employees.  You are not responsible for that job beyond giving the two weeks notice.  

If the company treats you poorly during the two week notice period, all you can do is offer to leave immediately.  In that case you may loose two weeks pay.

Thank your manager for mentoring.