By Andrew Gamble Phil Mickelson will delay retirement for as long as possible as the six-time major champion still harbours hopes of clinching the U.S. Open. Mickelson’s dream is to win the U.S. Open and complete the career slam. He’s finished second at the event on six occasions while winning three Masters titles, two PGA Championships, and one Open Championship. Although he’s no longer qualifying via the rankings as LIV Golf stars don’t earn ranking points, Mickelson should still receive invites from Augusta, USPGA and The Open as a former winner. He should also get an invite to the U.S. Ope…