Some mini v2s have issues detecting USB 2.0 devices. If the iphone uses USB 2.0 on its port then it may not be detected. It is a hardware problem that requires replacing a capacitor as detailed in this post.
I would test any other USB 2.0 devices you have such as flash drives, webcams, printers, etc. If they are not detected and do not show up when you run “lsusb” in a terminal, then that may be your problem.