Phillips, who was a regular in England’s team on their run to the European Championship final last year, sustained a dislocated shoulder in training last week and will undergo an operation, potentially putting at risk his place in England’s World Cup squad.
Liverpool midfielder Jordan Henderson has been added to the England squad for their upcoming Nations League matches against Italy and Germany. Henderson was not part of manager Southgate's initial squad after missing Liverpool's last three games in all competitions due to a hamstring injury but the club said he was recovering well.
"Henderson has made good progress in his recovery from a hamstring problem and is set to return to full training this week," Liverpool said in a statement.
The 32-year-old, who has won 69 caps, has made one international appearance this year in the 2-1 friendly win over Switzerland in March.
England face Italy in Milan on Friday, before hosting Germany at Wembley next Monday. The Three Lions have two wins and two draws from their four group matches so far. The Germany fixture is a final runout before they begin their World Cup campaign against Iran in November.
Among the players involved during training for the Nations League was Ivan Toney.
Brentford striker Toney is the only fresh face in the England squad. He was rewarded for his fine start to the season with five goals in seven Premier League games.
Manchester United duo Harry Maguire and Luke Shaw have been included in the 28-man squad despite losing their place at the club under Erik ten Hag.