I need my Mahler fix so don’t stand your phone in my way — OK. I get it. You’re a millennial, like my daughter, and a millennial’s idea of a concert memento is not some dog-eared concert brochure forgotten among rolled-up socks but a forgettable little video to post on Insta, TikTok, PicFlip, ShitPost, or whatever the thing is now. I’d look at you…