For years, Phil Mickelson has chased the one major that would complete his Grand Slam. An exclusive circle that includes Jack Nicklaus, Tiger Woods, Rory McIlroy, Gary Player, Ben Hogan, and Gene Sarazen.But after six runner-up finishes and decades of near misses, it looks like Lefty has convinced himself to let go.Mickelson had a disappointing show at the Masters, where he missed the cut, and another early exit at the PGA Championship. Now, with his U.S. Open exemption set to expire, the 54-year-old dropped a bombshell at LIV Golf Virginia."I haven't thought about it too much," Mickelson said when asked if he thought Oakmont might be his last U.S. Open."There's a high likelihood that it will be, but I haven't really thought about it too much," he admitted, leaving room for speculation.This will be Lefty's 34th U.S. Open appearance— credit to his 5-year exemption earned from the 2021 PGA Championship win, where he became the oldest major champion at 50.But beyond 2025, his road back looks uncertain.LIV Golf offers only two qualification spots for the 2026 U.S. Open—one for topping the 2025 season standings and another for sitting in the top three by May 2026.If Mickelson wants another shot, he'd need a dominant LIV season, which, based on his recent performances, and his age, feels highly unlikely.Before his supposedly final show at the US Open, the 6-time major winner will be swinging clubs at LIV Golf Virginia, which mirrors Oakmont's conditions. And Phil wants to focus on that, treating it as an unofficial warm-up."What I have thought about is how similar this week's course is set up to what we'll see next week," Mickelson explained."We have greens that are rolling 14 to 15 on the Stimpmeter, just like we will next week. We have contours, undulations—just like we will next week. I think it's a great way to prepare for next week."He continued, "Short game, touch, chipping around the greens, rough, speed, lag drills, and touch on the greens—all that's critical here. Same thing as next week. It couldn't be a better spot to get ready."A look at Phil Mickelson's US Open heartbreaksThe outspoken LIV Golfer's U.S. Open record is brutal. He's finished runner-up six times—including heartbreaks in 1999, 2002, 2004, 2006, 2009, and 2013, but never hoisted the trophy.His first heartbreak came in 1999 at Pinehurst, where he lost to Payne Stewart by a single stroke. The moment became even more emotional when Stewart (Phil's ex-caddie) famously told him:"Good luck with the baby. There's nothing like being a father!" This came just before Stewart's tragic passing months later.Then came 2002 at Bethpage Black, where Mickelson finished three shots behind Tiger Woods, unable to close the gap on Sunday.Perhaps the most painful of all was 2006 at Winged Foot, where Mickelson needed a par on the final hole to win. Instead, he hit a driver off the tee, found the trees, and made a disastrous double-bogey, handing the victory to Geoff Ogilvy.Reflecting on the challenge years ago, Mickelson admitted just how much winning the U.S. Open meant to him:"I think that if I'm able to win the U.S. Open and complete the career Grand Slam, I think that's the sign of a complete, great player. I'm a leg away. And it's been a tough leg for me."Now, at 54, the coffee lover faces the reality that his U.S. Open exemption is expiring, and his chances in front of the World No. 1, who is currently fully charged, are slim.But if history has proven anything, it's that Lefty has never been one to back down from a fight.More Golf: Bryson DeChambeau Seen Playing Golf at 'TPC White House