We could definitely see ourselves using the iPhone 7 Plus, portrait or not, more and more in future shoots. When most of the images we create are for online delivery, the resolution of the iPhone is already large enough for this purpose. Of course, for print or larger-format distribution, we'd need to use our standard professional equipment, but I don't think mixing some of the iPhone photos with professional equipment would create a problem for clients.
For travel photography for example, the iPhone could be particularly useful. Nature, landscapes, could all be captured pretty stunningly with this new camera on the iPhone 7 Plus. And it's great to have the new Portrait mode, for more specific usage scenarios, which as long as we are conscious about how we utilize it we can still get pretty amazing results.
Like we always say, it's the story that matters – the image, the moment, the capture. The tool is the least important thing, as long as we convey the meaning and emotion of the moment, and we make our clients happy. And that's the beauty of having the iPhone always in a pocket, with the professional gear nearby.