SLRs shine when there is more lighting range (e.g. strong shadows and light) in the shot and in particular when it is a lower-light situation. A smartphone has to start doing HDR (which has inherent downsides, like its inability to record motion) a lot sooner than a lot of SLRs as the dynamic range is wider on the latter.
You also lose physical controls and the ability to change lenses on a smartphone, which slows you down, and makes your shots look more samey. The viewfinder (either EVF or OVF) is also a huge benefit when shooting in either strong sunlight or extreme darkness (as the LCD's backlight can bleed light into your shot).
As to contrast Vs. phase detection: Contrast is very accurate for non-moving targets and even some moving targets (thanks largely to software). Phase detection is still the king of the castle when it comes to high speed and erratic motion however, by far.