There is much debate over this topic. Can your iPhone match the picture quality of a DSLR? Does it have the editing power of Photoshop? Well, obviously the answer to both those questions is a big fat no, but that aside your iPhone does have an amazing camera and you can do 99.9% of anything-- meaning, almost everything with it. I wouldn't recommend using it as your main source for photographing a wedding--but I would say the iPhone can do many things for everyday purposes, like blog photos or facebook photos and even marketing photos, like Etsy--and that it does these things very well. I would argue that if your doing it right only a professional will be able to tell the difference between your iPhone photos and say, someones DSLR photos. Oh, and did I mention it fits in your pocket, which is more then I can say for your DSLR.
A DSLR really does one basic things--it shoots pictures. Then you have to edit them on your computer. A iPhone shoots and edits, all in a few moments. So, how can you use your iPhone as a DSLR? Very carefully, of course, and utilizing the apps I show below.
To frame my photo I use Moldiv. It creates these lovely square/framed photos you see above and below.