It’s not really a flash. Stan Horaczek explains:
Smartphone camera flashes have a bad reputation—and it’s well-earned. No matter how hard companies try to bolster their on-camera illumination, the results come out smeary, oddly-colored, and often kinda blurry.
The LED light on your smartphone, however, simply turns on and off at a long interval, which leaves plenty of time for your subject—or the phone itself—to move while you’re taking a picture and introduce ugly blur.
I hate iPhone’s flash. Samsung is no better.