City won 4-1 on Wednesday night, with Foden scoring twice.
Afterwards, Guardiola declared the England midfielder was now back to his very best.
“This season he is back,” said the manager. “Not just Phil, all of us we struggled (last season).
“When Phil is in that level playing between the lines, in the pockets and his first touch, his turn and then after his generosity to run and fight (is exceptional).
“When Phil is happy with love and joy, you don’t have to say much. He’s a special player but we need his goals and hopefully today was the first step to do it.
“It’s important to have him for the big, big match on Sunday (against Liverpool).
“He’s important. It’s not like today he just came and scored two goals
“Two seasons ago he was the best player in the Premier League and when you do that in the Premier League it’s because you are really, really good.
“Assists, goals, work ethic and recovery. He’s a top class player and we missed him a lot, especially his happiness.
“We feel he is back and he can do whatever he wants.
“How many times have we seen Phil score these goals?
“It’s going to help us a lot for him to score these types of goals. Just put the ball close to the posts. It’s like a pass to the net.
“Phil is fantastic.”
We're improving
City are now in an excellent position at the halfway stage of the Champions League initial phase with 10 points.
“We are fourth and we are better than we were last season by far,” Guardiola added.
“We have to try to close it. Many days until Bayer Leverkusen but next step.
“Huge respect because three days after we play so demanding a team in Bournemouth.
“They limit you physically and mentally. It was tough but we handled it really well.”