The smartphone camera vs. SLR debate is eternal. Smartphone cameras have improved substantially, and it's possible that the OP's experience is with a manufacturing defect or some odd choice of settings. That said, my own gripes with smartphone cameras are....
1. They're hard to grip and hold properly.
2. Slow autofocus.
3. Poor performance in low light.
4. No lens interchangeability (obviously).
5. Minimal manual control, especially over depth of field.
6. Shutter (for lack of a better term) lag.
Assuming that the smartphone camera focuses on the right thing, at the right moment, with the right lighting, then results are pretty decent; they vie with that of "kit lenses" and consumer-grade SLRs. Even so, I have little patience with photography equipment reviewers who decry expensive lenses in untutored hands, as "compensation" or mindless performance chasing. Top-shelf equipment, within reason, makes a difference.
With respect, I would avoid mass-market zooms such as the Nikon 24-120 mentioned above. Stick with primes, don't be afraid of "vintage" manual focus lenses, and pay attention to technical data such as Modulation Transfer Function. Distortion can be corrected in software, but "sharpness" corrections are phony. If the lens isn't sharp to begin with (and the focus and so on, set correctly!), nothing will help the image. And yes, the lens matters far more than the camera body.
