The camera in the iPhone is fast and easy, but it's still limited to what it can do. If you want to step up the quality of images you're sharing on Facebook, Instagram, or any other social network with your fancy DSLR, then you would need to download the images to a laptop computer and hopefully have Internet Access. A simple approach could be to send it wirelessly from your DSLR right to your iPhone (which should already have Internet access).
YouTube member 1sicknickel shows how the Eye-Fi Wireless SDHC card works with the Canon 5D Mark III [Thanks Peter]. From your iOS device you'll connect directly to the Eye-Fi like a hotspot and see images taken with your camera. This is not exclusive to the Canon DSLRs, as it will work with many cameras (including many point and shoots). Check out the Eye-Fi SDHC cards via Amazon (Click Here).
Eye-Fi Pro X2 SDHC