Phil Mickelson's U.S. Open appearances, and his quest for the career Grand Slam, may be coming to an end this summer. Mickelson is in the field at the major championship next week at Oakmont Country Club outside of Pittsburgh. The U.S. Open is the last major that Mickelson needs to complete the career Grand Slam, which is something that Rory McIlroy just pulled off with his win at the Masters earlier this year. But Mickelson is in the final year of a five-year exemption into the event, which he earned for his win at the PGA Championship in 2021. Without another exemption, Mickelson will very likely have to start trying to play his way into the tournament. "There's a high likelihood that it will be [my last U.S. Open]," Mickelson said on Wednesday ahead of the LIV Golf event in Virginia,via ESPN, "but I haven't really thought about it too much." Mickelson, the once-popular and dominant force on the PGA Tour, has struggled in recent years amid his jump to LIV Golf. He got caught up in the feud between the two leagues — especially after hiscomments supporting Saudi Arabia, who he once described as "scary motherf***ers." Mickelson stepped away from golf for a while after that. Healso opened up about his gambling addiction, which plagued him for years. On the course, the 45-time Tour winner has not been great since his PGA Championship win. He's missed the cut in 10 of his last 14 major championship starts. The only exception during this stretch was a T2 run at the Masters in 2023, though he never really stood a chance to catch Jon Rahm at Augusta National that year and only surged up the leaderboard that Sunday. Mickelson has come close to winning the U.S. Open plenty of times in his career. He has six runner-up finishes at the event, most recently in 2013. He's made the cut at the U.S. Open just four times since then, and he's missed the last four entering Oakmont next week. Mickelson, who will turn 55 later this month, already has lifetime exemptions to play in both the Masters and the PGA Championship. He can keep playing at the British Open until he's 60, too. Mickelson has been leading the HyFlyers GC in LIV Golf since its inception, though he's currently No. 15 in the individual points standings. As for his future with LIV Golf — which still has not struck a deal with the PGA Tour despite years of negotiations — Mickelson only wants to keep going as long as he's productive. "This year I've played better," Mickelson said, via ESPN. "I feel like I've held it back the last couple years. I had a great offseason. I don't feel I'm holding it back now. If I can continue to play well, help the team succeed, then I want to play. But if not, I'm also realistic and I want the team to succeed more than I want my own personal interest [in] playing."