Coutinho signed a new long-term deal with Liverpool this week to end all speculation about a potential move to Barcelona.
Gerrard, meanwhile, is set to return to Liverpool as a youth coach, a role he will start in February.
And, speaking at the launch event this week for the Star Sixes tournament, to be held at the O2 Arena in London in July, Gerrard said of Coutinho: "I think for any team you have always got to try and keep your best players and Philippe has been instrumental over the last couple of years.
"He has grown and become a world-class talent.
"I have trained against him on a daily basis and played with him and he is a phenomenal footballer. He can do magical things with the ball.
"He is the type of player you want to build your team around. And if Liverpool are to be successful in the coming years then I am sure he will have a big part to play in it.
"He is a magical player."
Liverpool crashed out of the EFL Cup in midweek as Southampton proved to be too strong in the semi-finals, but Gerrard remains confident they can win silverware this campaign.
"Of course they can win trophies this season," he added.
"They have had a sticky period but they can certainly play through that. I think the next two or three games are very important. If they can get a win against Wolves they can go into the last 16 of the FA Cup. If they can take maximum points off Chelsea it gives them that bit of confidence and belief. So there is still a lot to play for.
"But I think the big picture for Liverpool is exciting. They have got a very strong team, strong squad and a world-class manager so I expect big things."