There will list some difference between mobile phone flash and camera built-in flash.
1) Most camera flashes use Xenon flashes and most of mobile phone use LED flashes.
2) The Instantaneous power of Xenon flashes are many times more than mobile phone flashes. Take example, if you watch the Xenon flash directly, it may make you blind. But the light of mobile phone flash is soft and sometimes it can used as flashlight.
3) The power consumption is different. LED flash can keep lighting for a long time but Xenon flash needs to wait a moment to uses again after you use it.
4) The light of mobile phone flash is soft, and it can help a lot in optimizing portrait. Xenon flash’s object is to get more exposure, and the light is harder than mobile phoneflash’s. Therefore, the external flash needs to be used with diffuser, reflector for a better photographic results.