Most phone camera features inadequately mimic DSLR functions
The flashes on cell phones aren’t actually flashes in a real sense -- they’re tiny flashlights. A flash is a quick release of energy -- sometimes as fast as 1/100,000th of a second -- that allows a much greater light output with less power required and heat generated. Not only are they stronger, but that fast triggering freezes motion even when the camera has a low shutter speed, opening up a slew of opportunities for capturing action. For now, at least, this alone opens up an entire photographic world that can only be approximated by even the best cell phone cameras.
Lastly, to maintain size, there are only certain kinds of lenses that you are going to see. Adding a real optical zoom increases size, and you’re not likely to see a 28-300mm equivalent lens on anything that looks like a phone any time soon, at least without additional clip-on lenses that reduce optical quality to some extent. You’re not going to capture far-off birds in flight, or shoot a soccer kick-off from the sidelines.
I don’t even need to say that you can create an amazing photographic portfolio using only cell phone cameras -- countless people are out there doing it right now. But there will always be areas where it just pays to go bigger, particularly when looking at technically difficult fields like low-light action. Technically, interchangeable-lens photography is already a niche, due to the staggeringly high number of smartphone photos. But it is a rewarding, irreplaceable niche rightfully loved by millions, and it’s not going away anytime soon.