Pretend that you're reading something, then bring the phone up to your face, as though you just read something weird that you have to read again, and take the shot at that moment. That will get you a better angle. Or, act like you're scrolling through a list. People seem to tilt their phone more when they scroll. Or, if earplugs are attached, act like you're fiddling with them in their connection. That lets you hold the phone perfectly vertically.  Finally, ALWAYS ensure that the flash is disabled. I sometimes do a photo of my hand first, just to test; can't be too careful.