The midfielder is still part of the WhatsApp group for his old club, despite making a £42million move to Man City this summer.
It seems that Phillips can't quite let go of his boyhood team just yet, having spent the last 12 years at Leeds.
The England international recently admitted that he had not left yet and was still one of the admins along with Cooper.
The Leeds man spoke to talkSPORT this week and admitted he may have to have an awkward conversation with Phillips.
Cooper told talkSPORT: "He is [still in the group]. I feel like Kalvin is family, it's difficult to just bin him off in that way.
"If I do bin him off, I'm going to have to be a man and ring him and say 'you're going to have to go'.
"I'm going to speak to the senior players and see what the craic is.
"Kalv might do us a favour and just leave himself. He's making me make a big decisions… we'll see."
talkSPORT host Ally McCoist urged him to boot out Phillips from the group as he is gone, and was shocked that Alan Brazil and Stuart Pearce seemed happy for him to stay in there.
He told Breakfast: "Out! He's got to go. I'm shocked at you, Pearcy [Stuart Pearce]. How can you keep an opposition team member on board.
"He's out!
"He's got to go. You can have a wee private WhatsApp group with him, but he's got to go [from the team one]."
Cooper did also wish Phillips well following his move to Premier League champions Man City.
He added: "I've been with Kalvin since he was 16 or 17 years old. What a beautiful man he has grown into, and what a player he has grown into.
"They [Raphinha and Phillips] go with our best wishes. We are gutted to lose them, it's so hard for any team to lose your two best players but they go with our best wishes and it's a new era for us."