Phillips was introduced on 51 minutes against Forest shortly after fellow defensive midfielder, Rodrigo, was red carded.
The England midfielder put in a fine shift to help us to three points despite the man disadvantage for the sky blues.
The boss was happy with what he saw and praised the attitude of the former Leeds man during a time when his opportunities have been limited.
“He played really good today,” said Guardiola.
“For the type of game that we needed, defensively and keeping the ball and run, he was amazing.
“I’m so pleased for him because he’s an incredible guy, never one bad face when he didn’t play the minutes.
“I know he’s a player for the national team of England, and with me, with us he doesn’t play much. But he played really good and helped us a lot.
“I know sometimes he struggles for some things that we need, in small spaces to be quicker, and other ones has another type of quality.
“But in the game today, what we needed, to be there, to win the second-balls, to keep the balls, to make actions to the by-line, the personality in long balls, even in the corners, because we knew it with a lot of crosses in the way they play, he gave us a lot.”
Nunes made his third appearance for City in the weekend victory at the Etihad – and it was his second start in succession following an impressive performance in the 3-1 victory over Red Star Belgrade on Tuesday.
Guardiola quizzed former Wolves boss Julen Lopetegui about the midfielder before his summer transfer and was very happy with the reports he had back.
The boss has been delighted with what he’s seen of Nunes since the move to City and believes he has more to offer in the coming days, weeks and months ahead.
“Really good,” said the boss.
“Sometimes he has to stay more calm in the position, but he has the dynamic.
“In the game today, give the ball, dribble, and drop the opponents down.
“He looks like he’s never tired, because his actions over 15, 20 metres – but we knew it from Sporting Lisbon where he has done it, as well as at Wolves.
“We asked [Julen] Lopetegui, who is a friend of us, how is he, and all the opinions were really good.
“He has runners, good finishing, defensively [he] can play in two or three positions.
“The last two games he played against Red Star and today, he was a key point - really, really important.
“He’s an exceptional player, exceptional.”
Watch part two of the manager's post-match press conference above.