Southgate is currently preparing for his first match in permanent charge of the Three Lions after impressing during a four-game interim period last year.
The former Under-21 boss has recalled Defoe to the national squad, and the Black Cats forward has praised Southgate ahead of Wednesday's friendly with Germany.
The 34-year-old told reporters: "I had a conversation with him on the phone. He is someone who has always impressed me. I remember playing against him.
"He is genuinely a really nice man and someone who I believe will do well because he has been there and done it, he has played in major tournaments. He is fully equipped to handle the pressure.
"I think it's refreshing for a player to have a manager in front of you who has been there and done it so it's good."
As well as the trip to Germany, England also host Lithuania in a World Cup qualifier during the international break.