The six-time major winner is in Chicago for the fifth event of the inaugural LIV Golf Invitational Series, and was speaking to the media after carding a two-under-par 70 in Friday's opening round.
Since launching in June, the PGA Tour has done everything in its power to stop the encroachment of the breakaway series, which has no shortage of money to throw around thanks to being bankrolled by Saudi Arabia's Public Investment Fund.
But Mickelson reckons they are fighting a losing battle, and the days of them enjoying a monopoly are over.
"The PGA Tour, for the last 20 or 30 years have had all the best players in the world. That will never be the case again. LIV Golf is here to stay," he said.
"The best solution is for us to come together. I think that the world of professional golf has a need for the old historical 'history of the game' product that the PGA Tour provides. I think that LIV provides a really cool, updated feel that is attracting a lot of younger crowds.
"Both are good for the game of golf and the inclusion of LIV Golf in the ecosystem of the golf world is necessary. As soon as that happens, we all start working together. It's going to be a really positive thing for everyone."
Players who joined the LIV Golf series are no longer eligible to participate in PGA Tour events, while LIV golfers are not currently able to earn points towards the Official World Golf Ranking system.
Mickelson believes the only solution is for the two parties to learn to live together, but LIV Golf CEO Greg Norman no longer seems interested in talk of a truce.
"We have no interest in sitting down with them, to be honest with you, because our product is working," Norman told The Australian in an interview earlier this week.
Two-time Major champion Dustin Johnson holds a three-shot lead at Rich Harvest Farms in Chicago after opening with a 63.
New arrival Cameron Smith of Australia was second on six under, with Matthew Wolff a shot back in third.