I have two professional cameras and have had others in other brands before, none of them have built-in flash (and in fact I don't think any semi-pro or pro camera have built-in flashes). There is one main reason for dropping the flash: if you want extra light to expose your pictures, you have to do it properly, i.e., not with the limitations that come with built-in flashes, so you'd better off dropping the features that won't be up to that standard and still come at a cost.

Of course phone cameras are not the same, nor do they serve the same purpose, and it's arguable that a flash could be more useful on a phone since the main purpose of the camera is to take souvenir shots rather than artistic pictures. Plus their sensors do not show the same performance in noise control. I acknowledge that. But if we come by that definition, there's little support for justifying the bulk of a xenon flash and design/power supply issues it brings, a LED flash should be plenty enough for taking a souvenir picture, and even the best (!= powerful) flash won't do miracles when placed 5 mm next to the lens right in front of the subject.