Green light when videoing at concerts

That is normal Lens Flare. It's almost impossible to eliminate, especially when videoing a concert which is recording in a low light environment WITH bright lights, which are reflecting off the camera lens. Even my expensive Nikon DSLR, with a lens costing more than my iPhone by a lot of money would do the same in such an environment.

Now, had you had your phone mounted on a tripod, where you could angle the cameras appropriately to avoid the lens flare, that would have been the only way to avoid it. Otherwise, holding a cell phone in a place like that and moving it about, would be a prime way to capture lens flare.