If you shoot a lot with your iPhone you might want to take a look at the 645 PRO photography app. According to DPReview Pro 645 “intercepts the camera data after it’s been initially processed (demosaiced and with processing parameters such as white balance and sharpening applied), but before the phone compresses it.”  It also allows you to save the file as a TIFF.  Read more at DPReview or buy it from the App Store.