I went for a walk one morning with my new iPhone14 Pro Max, and myDSLR (Nikon D500). I noticed a few things.
TLDR; cell phone cameras are designed for taking pictures of “things” and are pretty good within their limits.
The first thing is that the iPhone (and most phones) prefer wide angle lenses. I know there are a few cameras that have up to 10x (at time of writing) lenses, but these longer lenses are usually lower quality. Another difference is that each lens has a different sensor, With the iPhone, each of these mini cameras (sensor and lens) is pretty well matched in terms of colour balance. But sensor size and resolution are different. On a DSLR, not only is the sensor MUCH larger than all of the iPhone sensors put together, it is used for any lens you put on the camera. And of course there are way more available lenses for a DSLR, including real zoom lenses. I am not aware of a cell phone that can actually zoom the lens. they “zoom in” by cropping (digital zoom) or switching actual “mini cameras”.
Another difference is looking at a screen vs looking through a viewfinder. I find it much easier to fine tune composition using the DSLR viewfinder, however I can see some advantages to seeing outside the image area, especially for action shots. A DSLR can also work in “live view” where you compose on the back screen of the camera, and that is useful in some situations (like on a tripod) but it is secondary.
If I want to fine tune my composition, ie control exactly what is at the edges fo the frame, I found it easier with the DSLR viewfinder. It might be that I am more used to a “real” camera, but I found the iPhone shows the scene around the final image, like an old school rangefinder. That is one reason I never really got into compact cameras, or even more serious rangefinders.
Looking through a viewfinder removes any distractions around you as well. I find I can relate much more intimately with the scene I am trying to create. Using a screen (phone or live view) involves the rest of what is going on around you. That can be great if you are recording a friend, or even an object where the background is not important, but if you are trying to create a whole image composition, I find it tougher (Have I said that too many times yet?)
As for image quality, at web resolutions, they are pretty close. The iPhone does a bit more processing, but I do processing on my images anyway. I am not sure how the phone images would work as a large print, without a lot of work.
Interesting experiment. Like a lot of things, each tool has strengths and weaknesses. I can see times when the light weight of the phone will outweigh some of the advantages of a DSLR. As I said above, if you just want a record of a place or person, a cell phone is more than adequate. If you want to produce a fine art piece on a consistent basis, or you want more precision, or you want more versatility, then a DSLR is probably the best option.