Alongside Declan Rice, the Leeds United man has become a mainstay of the Three Lions midfield, earning 17 caps and playing all but 25 minutes of the Euros en route to the final.
That game against Italy, which was lost only on penalties, is one of only two occasions when Phillips has experienced defeat in an England shirt.
Southgate, who felt the 25-year-old's yellow card in the 1-1 draw with Poland was 'harsh' on first viewing, is delighted with Phillips' adaptation to international level.
"He's been excellent," said the Three Lions boss.
"The way he has taken to international football, it hasn't surprised us because what we'd seen with Leeds, even in the Championship, we felt could convert into our team. We felt he could play an important role with us."
Phillips not only experienced a major tournament in his first year as an England international but huge Euro 2020 games against Germany, Denmark and Italy. His performances were rewarded with the England Player of the Year award and the appreciation of his manager.
"To play in the enormity of the matches he did in the summer and play as well as he did is massive credit to him," said Southgate.
"He's a very, very good player and he's been a really important part of this - we're 16 games unbeaten [in regulation time] now and he's been a huge part of that."
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