Barkley is back in the England squad for Wednesday's friendly against Germany and the upcoming World Cup qualifier against Lithuania for the first time since Euro 2016 after impressing Southgate with his performances in recent months.
"He is a player who really affects the game around the penalty box," Southgate said of the attacking midfielder.
"He has great creativity but also power around the penalty area. That is important, especially if you are playing against teams who are banking up or packed defences.
"You need players who can maybe beat someone one-to-one and he has the strength, the power and the guile to do that. But also the other day against West Brom a couple of lovely floated passes and chips over the defence. He is quite an instinctive player and also exciting.
"He is playing a slightly different position for Everton in the last few weeks. He is playing on the right but drifting into the number 10 slot which is where he does his best work.
"I think physically he looks in slightly better condition and Ronald Koeman has talked quite publicly about the things he has asked him to do. I just think he is in a better moment as an individual player and playing with confidence."