Leroy Sane scored twice as Manchester City came from behind to beat the Bundesliga outfit 2-1 at the Etihad Stadium on Wednesday and secure top spot in Group F.
Highly-rated teenager Foden shone in midfield, particularly as City took firm charge of the game in the second half, having been given a long-awaited opportunity by Guardiola following a spate of injuries.
The 18-year-old almost got on the scoresheet himself when he forced a fine save from Oliver Baumann with a fierce left-foot volley.
"Phil was incredible, the way he played," Guardiola said. "I would never have doubts about the quality of that guy. It is not just the quality with the ball. He looks skinny, not strong, but he's really, really strong.
"He's an outstanding young player, a huge talent. I think England has a diamond. He's special, he has had minutes and in the future will have a lot of them.
"He played like a real man. He played so good."