It was, in almost every respect, a carbon-copy weekend gig for Josh Walther and his wedding band, Phase5. Booked a year in advance at a familiar Winter Park country club. Intimate, 200 people, tops. Decent vegan spread."The decor wasn't extravagant," he said. "It was just a typical family gathering."Totally typical, yes — except for the part where Paul McCartney showed up. And hopped onstage. And grabbed the microphone. And sang I Saw Her Standing There. And left Walther and his band reeling from the musical memory of a lifetime.It's a bucket list moment for any musician, sharing the stage with Sir Paul, and when you play in a wedding band from Tampa, it's one you're 99.999 percent sure you'll never experience. But it happened on Saturday for Phase5, who played the graduation party of McCartney's stepson Arlen Blakeman, a communications major at Rollins College in Winter Park, just north of Orlando. A clip of the performance hit Facebook and YouTube over the weekend, and Walther, 33, has since been inundated with kudos from everyone he knows, and many more he doesn't. "He's at the top of the food chain for every artist and musician," Walther said. "I've been told since that he doesn't ever do that type of thing. It's very rare. I think that's why a lot of people are contacting me and posting it, because he doesn't do that that often with a band he doesn't know. I was really surprised. I never thought that would happen."Surprises are rare in the meticulously planned life of a cover band. Phase5's weekends are booked ages in advance, typically through word of mouth.McCartney's wife, Nancy Shevell, discovered Phase5 while researching event bands in Florida, Walther said. She liked their look, sound and website and called about a year ago, asking them to play a graduation party for her son from a previous marriage. Not knowing anything about Shevell, Walther initially said no — Phase5 doesn't play many graduations, and they were booked for a wedding that day. But he kept her number, and when the wedding got moved, he called back. They settled on the band's usual four-figure rate.It wasn't until March that he realized what a smart decision that was. He was in Home Depot, buying sponge mops and paint for his new downtown Tampa condo, when Shevell called to talk specifics about the gig — what time they should arrive, how many meals they'd need, what kind of sound equipment they used. "She was asking me detailed questions about what kind of mics we use," he said. "I said, 'You really know a lot about sound equipment.' She's like, 'Well, yeah!' Then she mentioned she was Paul McCartney's wife."A stunned Walther wandered away from his shopping cart.She asked, did he know of McCartney?"Yeah, of course I do," said Walther, often mistaken as younger than he is."Oh, because of that Rihanna and Kanye song?"Although Phase5 has played weddings and parties with celebrities in the audience, nothing prepared Walther for the sight of Sir Paul on the dance floor at the Interlachen Country Club while he filmed his band with a camcorder. When Phase5 broke for intermission, McCartney rushed up to say hi."Hey, man, would it be cool if I sat in on a couple?" he said, according to Walther."Uh … yeah? It'd be cool," Walther said."Do you know any of the Beatles tunes?" Walther was dumbfounded. "It was almost as if he was introducing himself, as if we didn't know who he was."Walther rattled off Phase5's Beatles playlist: Yesterday, In My Life, Come Together, Can't Buy Me Love. McCartney asked if they knew I Saw Her Standing There. Walther admitted they didn't — Macca, he said, was visibly bummed — before pianist Stephen Dornfeld jumped in and said they'd give it a shot.On top of that, McCartney asked if the band could make up a bluesy song on the spot. "Basically," Walther recalls him saying, "I'm gonna sing a line, and then whatever I say, at the end of the line, you'll just repeat. If I say, 'Graduation!' Then you'll repeat, 'Graduation!' Like they did in the old days."So now, in addition to playing a Beatles song they didn't know, Phase5 was actually crafting an original song with McCartney. Perfect."The whole time, I'm thinking, 'This is gonna be a disaster,' " Walther said.But it wasn't. For 12 minutes, the band held their own alongside a Beatle, and the crowd reacted, well, exactly as you would react if Paul McCartney just hopped onstage at your graduation party. Afterward, he was very complimentary, Walther said."He told me I had a really smooth voice."After the show, the musicians sat around, awed, thinking about what they'd just done and where they'd go from here. This week, it's back to the grindstone in Tampa — more parties, more weddings, a standing Thursday gig at Eddie V's, a slot opening for Smash Mouth at next weekend's Tampa Bay Margarita Festival.Packing up their gear took longer than usual, Walther said."I'm putting away this mic," he said, "thinking, Paul McCartney has used this mic. Every best man at a wedding from now on that's giving the toast, he's going to use this microphone that Paul McCartney used."Contact Jay Cridlin at [email protected] or (727) 893-8336. Follow @JayCridlin.