Use iPhone camera as an input sensor for EV3
I haven't come across any existing projects like this yet, but there is nothing stopping you from doing this yourself. I would suggest writing an app for your phone in Obj-C and just remote controlling the EV3 via bluetooth.

The bluetooth communication uses the RFCOMM profile. This post might give you some hints on getting the bluetooth connection.

You can find the EV3 communication protocol specifications in the hardware developers kit that is linked in this blog post.

Hopefully this is is enough to get you started.