As summer settles in, the Plymouth Philharmonic Orchestra invites audiences to leave their worries at the door, slip on their flip-flops, and head for the islands — no passport required. The Phil’s upcoming It’s Tropical Rock concert, June 27 and 28 at Memorial Hall, 83 Court St., will feature the music of Jimmy Buffett, Bob Marley, The Beach Boys, Bobby McFerrin and other icons of laid-back summer listening. Postponed from February by a winter …