I'm extremely conflicted on this issue. I strive to not be a hypocrite as much as possible so in this try to constrain my activities to a set of rules that I would be comfortable with everyone else following. SO here's where I'm at:
I go to a LOT of concerts. I believe the vast majority of people don't understand the depth of this statement. 5-7 nights a week. 250-300 days out of the year I'm seeing live music. There are many different kinds of shows and each one has slightly different rules. Clubs are very different from Theaters are very different from Stadiums are very different from Festivals. You really need to respect the environment you're in. I really hate how a lot of people use their phones during a show BUT at the same time my favorite hobby, aside from seeing the music in the first place, is capturing it for the many many people who live vicariously through my concert experiences. This is not vanity. I get thanks on the daily from people who don't have the time or money to go see what I do and truly appreciate the photos and videos I capture and share. SO, I need to find a balance between getting that done and not being "that guy" at a show either. Here are the rules I try to follow:
1) Turn off your flash. *Period. Cell phone flashes suck. You will get better photos with the light that is being provided by the stage light engineer. The *only time you need your phone flash is if you are taking pictures of your friends in the audience and then only if they are in the dark (see #2). Your friends look cooler if you take a photo away from the stage so they are illuminated by the stage lighting anyway.
2) I don't take selfies or group shots during shows: This is not only obnoxious for the flash that is often used (necessary or no) but also for the "sorry we're going to expand and shove you all out of the way so we can get an unobstructed shot". I'm not going to say I've never been in such a shot nor taken one but I avoid it to the max because I hate it when it happens.
3) Keep video to a minimum: I love having videos but hate taking them and it's really hard not to be "that guy" while doing so. Aside from the above *never use flash while recording because goddammit why are you blinding me for that long! but also: a) Video is better horizontal than vertical. b) try to not hold the phone blocking everyone else's view. This is prime if you can be close enough that you can hold your phone over someone's shoulder so only you and maybe the couple people immediately behind you can see it. c) Phone video only looks good when you hold the phone extremely still. If you can't do this then don't record video. d) (Personally) since I want this to be worthwhile to the general public I always record a entire song. I don't want to watch some crappy minute long shaky video of whatever so if I'm going to go through the hassle and aggravation of recording one then its going to be steady, quiet and a complete song. I also shoot for no more than 1 video per show or set if any.
4) Do your work quick and go away. Block people's view for as little time as possible and put your phone away. I've had shows where I took literally hundreds of photos and the people around me were like "dude I rarely saw your phone in the air". Look for a good shot, get your settings configured when the phone is out of view, pop it up and take a few quick shots (this is faster when the flash is off and any HDR is off as well!) and put the phone away. ALSO you're not going to capture the whole show. Don't try. Take a bunch of (near most) songs off and just enjoy them. I've been behind people who were shooting constantly and it's annoying.
5) Don't do a bunch of other stuff with your phone. If it's a really major show I might do a single FB update with a photo but else my phone is in my pocket unless it's being a camera or watch. *exception: for really large shows (festivals / stadiums) people may need to find where I am / vice versa so texting is a necessary evil sometimes BUT I'm not sitting there chatting about other crap. Purely logistical stuff.
6) ALL of this only works well if you're close to the stage. At a stadium or other large venue show there are great wide-angle shots to get and honestly you're not blocking most people's view so shoot away BUT I'm always close to the stage and if I can't get close enough for my phone pics to look great then I'm just not taking them. Cell phones do NOT look good if you use your zoom (unless you have one of the *extremely rare phones that has an optical zoom on it) so if you have to zoom then you're too far away. Just don't take the picture.
There are some smaller shows where friends of mine in the bands I'm seeing will ask me to record certain songs for their purposes and I'll push these rules a bit for a business job. Specifically more video and both videos and photos almost always look better when recorded from high at a down angle. I'll still try to put myself in-front of a pole or out of the way so I'm not wrecking anyone's view more than necessary but if the band wants a video then, sorry-not-sorry, I'm putting their desires above yours for a bit.
FYI I've been at a few shows lately where phones or at least the use of them was banned. Dave Chappelle had the secure phone sacks. I avoided using one but still kept my phone away for all but a very secretive single "I was here" shot. Amon Tobin and Puscifer had lots of security making sure your phone never came out.. mine stayed in its pocket. The late, great Prince was absolutely vicious about no phones at his events. You had to leave them in your car and any, even slight, violation resulted in ejection so not worth it. In-general always respect the artist. It's their art to let you, or not, record/capture.