As a practical matter, legitimate agents and publishers do not make "cold calls" by phone or e mail. They expect you to go to them. There may be very rare instances where an agent or publisher takes note of a self-published book that is selling very well, but not on a book no one has bought. Either work with a legitimate agent if traditional publishing is your goal, or else stick with self-publishing and don't trust anyone you don't know and haven't vetted personally.