Coutinho committed his future to Liverpool by penning a five-year contract this year and, speaking at a news conference ahead of the Premier League Asia Trophy final against Leicester City in Hong Kong, Klopp was reluctant to entertain the prospect of one of his key men departing less than a month before the 2017-18 season kicks off.
"Yes, we can say that [he's not for sale]," the manager said.
"But this is not just since this morning or yesterday - I'm not sure it was different at any time.
"I'm not surprised that any club is interested in players of Liverpool. I think a few people in the room are more surprised. It's not a compliment, it's obvious that people see we have good players.
"But a very important message maybe, is that we are not a selling club.
"We believe in working together, we believe in developing together, we believe in using our basis, we want to make the next step together, and for this, we need to stay together."
Klopp made no attempt to disguise the importance of the Brazil international to the Reds, who missed Coutinho during a period the playmaker spent on the sidelines last season with an ankle injury.
"Phil is a very, very, very important player and we need to react better when he's not on the pitch," he said.
"When he was out and came back, he was not in the best shape and had to get back into his rhythm and with his quality, he has all the pressure to perform on the pitch.
"Other players you can keep them in training and hide them a bit, but Phil, when he's able to run properly you want to have him on the pitch again so he has to be better even in moments like this.
"He can improve with his consistency, but there is no doubt about his quality. He's got good movements, he's very smart in both aspects of the game - offensive tactics and the defensive. That's really important and he's still a young player who can improve. He's improved a lot since I've been here, he was good before of course and is in a good way."
Coutinho's main creative ally in Klopp's Liverpool line-up, England international Adam Lallana, believes his team-mate is happy on Merseyside – even if he does possess the quality to shine on Barcelona's grand stage.
"He's a fantastic player," Lallana said. "It's not a surprise that teams are interested in him. He's definitely happy here.
"Philippe is in that elite bracket. There's no reason why he can't achieve huge things here at Liverpool."