|Add-on lenses for the iPhone have|
proved to be popular.
On the iPhone 6 this appears to be more of a raised ring around the lens, which doesn't, at first viewing, appear to serve a purpose.
However, if it's there, it's there for a reason. And being around the camera suggests that it's there for the purpose of mounting lenses or filters. We've seen any number of clip on camera systems for the iPhone and I'm sure that Apple probably sees some potential to draw on that market. Creating a new standard for lens and filter mounts specifically for the iPhone allows Apple to further enhance the ecosystem that it has built up around it's smartphone.
How this raised ring helps to mount these lense I'm not sure - whether it's a question of providing a location mechanism to centre the lens or whether the ring has a ferrous component to allow the magnetic connection of the add-ons I'm not sure.