Cameraphones will give you a 'reasonable' quality image, suitable for web posting, under good lighting conditions. That's it.
A DSLR will give you;
- the ability to shoot in raw
- full manual control over exposure
- very fast focuscapture rate (no lag)
- huge sensor which gives better low light performance & higher resolution (= large prints, up to billboard size in most cases)
- ability to control off camera lighting incl studio lights
- range of optical superior lenses tailored for specific uses
- abiltiy to add filters to allow for eg long exposures in daylight (ND filters)
- much greater range of apertures from f1.2 to f32
- shallower depth of field achievable
- longer shutter speeds including bulb mode for long exposures and night photography
- a viewfinder so that you can properly frame (& hold the camera more stable)
- tripod mounting so you can keep the camera steady.
That'll do for starters