This. to quote my father (who is actually a professional photographer): Pissy lens; pissy photo.

You need chunks of glass at the moment regardless of sensor size. I carry a basic DSLR around with me (D3100) and a decent but cheap lens (AF-S DX 18-55) and a shit smartphone. They cost less than a good smartphone and the results are amazing.

I was under the impression that there are basically not enough photons at the sizes that most smart phones sensors are. Once you get to low light levels a tiny sensor just can't be fed enough photons to give a good picture.

That's basically it but the amount of light reaching that sensor is improved by a somewhat larger lens than you usually get on a smartphone.

Sure. The more glass you have the more photons you can gather. I have a f1.2 50mm lense and the amount of photons it can pull in is amazing. There is no way any phone is going to be able to replicate this.

For a given exposure duration.

Unfortunately, things move.

Lenses have to be a certain size of the sensors and apertures are a certain size. And those sizes are fixed, for a given image (with a specific depth of field etc). So physics (the optics) is a thing. A breakthrough in optics that removed the need for heavy glass to bend light would be a revolution.