SUBMITTING PHOTOS THROUGH IPHONE

As noted by Test Screen Name, Adobe isn't looking for snapshots from mobile phones, thus there is no way to upload directly from the iPhone, and it's unlikely that they will provide such an app in the foreseeable future. It goes against their strategy of accepting only high quality images, and would flood the Moderators with poor quality snapshots. We've seen many, many rejected mobile phone images here in the Forum because, in general, they don't meet Adobe's quality standards. If you shoot in RAW, which is highly recommended, those images require editing prior to upload. And they require careful inspection on a large screen to weed out the images with flaws. 

Where do you plan to do the retouching and adjustment which almost every photo needs? Most people do this in Photoshop or similar on a Mac or Windows computer. It's not impossible to use photo editing on a phone, but since you will have to examine the whole picture in detail and high magnification it's likely to be pretty tedious.  Also, were you also planning to use the phone as a camera? Again, not impossible for a skilled photographer with careful subject selection and a tripod, but Adobe Stock aren't just looking for lucky snapshots.