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."
We’ve gathered the best of today's Premier League speculation below…
1. Clarets keen on Bryan
Burnley have been named among a number of sides who are believed to have been keen on free agent Kean Bryan, but ultimately missed out on the now-West Brom defender. He racked up over 1000 Premier League minutes for Sheffield United last season. (Birmingham Mail) (Photo by Gareth Copley/Getty Images) Photo: Gareth Copley
2. McLeish backs Leeds to abandon O'Brien deal
Alex McLeish has tipped Leeds United to make a move for a new midfielder in January after failing to sign Huddersfield’s Lewis O’Brien. (Football Insider) (Photo by George Wood/Getty Images) Photo: George Wood
3. Munoz opens up on Toon move
Newcastle United loanee Santiago Munoz has revealed he's not feeling the pressure to succeed at St James' Park, claiming he has a "calm" mentality. He's also expressed his desire to succeed and land a permanent deal. (Sport Witness) (Photo by Hector Vivas/Getty Images) Photo: Hector Vivas
4. Real interested in Carvalho
Leeds United and West Ham want Fulham starlet Fabio Carvalho, but could face competition from Real Madrid. (Daily Mail) (Photo by Jacques Feeney/Getty Images) Photo: Jacques Feeney
5. Toon eye up Berge
Newcastle United are monitoring Sheffield United midfielder Sander Berge as they weigh up a January move for the 23-year-old. (Football League World) (Photo by RUI VIEIRA/POOL/AFP via Getty Images) Photo: RUI VIEIRA
6. Rice wants out
Declan Rice is keen to leave West Ham next summer amid interest from Liverpool and Manchester United. (Eurosport) (Photo by Michael Regan/Getty Images) Photo: Michael Regan