SEOUL  –  Kicking off their global tour in the South Korean city of Incheon, the five members of K-pop boy band Cortis saunter onto stage in casual, streetwear-inspired outfits, exuding an effortlessly cool vibe.  “Put your phone down,” one of the members bellows. Piercing screams erupt. A sea of illuminated screens flickers back. “I told you, put your phone down,” he repeats, louder this time. Some fans do just that, but the packed stadium vibrates harder with cheers as thousands of phones stay in the air. It’s hard to say how serious this theatrical command is. “Put your phone down” is also the name of Cortis’s ongoing concert tour, which started in Incheon on 18 July and will head to cities like New York and Los Angeles before returning to Seoul later this month. The refrain reflects a message the band has long pushed: that fans should stop watching concerts through six-inch screens and engage with their performances in real life. It’s drawn mixed reactions from their fandom: fan-filmed content is a valuable social currency in K-pop. Park Ji-yeon, for one, could not bring herself to stop recording Cortis’s performances. The 22-year-old had specially rented a new, top-tier smartphone for both days of the Cortis concert just so she could film in the highest quality.

“I was standing right at the front, and I couldn’t bring myself to put my phone down because I don’t know if I’ll ever get this opportunity again,” she tells the BBC.

“I usually film concerts because I know a lot of those memories will fade as soon as I leave the venue.” While fans like Park continued to film, some heeded the band’s call. Kim Ga-eun, 25, who was seated in the amphitheatre-style venue, saw it all. “People in the back of the standing section were having a great time dancing together. I thought that really reflected the intention behind the concert,” she says. Cortis has had a whirlwind year since debuting last year under record label BigHit Music – part of the company that created pop sensation BTS. Most of its members are teenagers. The oldest of the group, James, is just 20 years old.

Their music videos have each amassed millions of views. Over the weekend they performed at Lollapalooza, the famed music festival in Chicago.