This was a potentially hopeless project of a few months ago but I was pleased with the result. We had seats high up and I was able to hold my phone with elbows on knees which meant I could film without being intrusive and I didn't need to look at the screen much. I could enjoy the real thing instead!
My iPhone X clearly isn't ideal at night, especially with cloud/drizzle but most scenes are ok. I didn't want to film the whole thing and I knew that when I did shoot I'd need to capture complete sequences of music. I used the 2x lens quite a bit and could in theory get another 2x by shooting in 4K and publishing in 1080 (not so good quality in poor light though). I tried to shoot some b-roll but the opportunities were limited from that position.
In editing I concentrated on putting a medley of complete musical sequences on the audio track. I'd add it to the video track first then tripple tap to separate the audio. Then I'd overlay some parts with “b-roll”: 2x zooms, background shots, crowd shots etc. I probably should have run it all through DeShake stabilisation but didn't because it would have taken an age. There are a few sequences where I had to cheat and the video isn't strictly matched to the audio.
This was a fun project to edit and the result is reasonably atmospheric I think.