Hi I can suggest a couple of FPV kits for you that are very small. However they transmit analogue video so are not directly compatible with your iphone, so you will needs to use a FPV monitor.screen to view the video in real time.
For viewing the video in real time my personal suggestion would be to buy the black pearl FPV monitor as it has built in batteires and receivers so its all self contained unit. It also has an integrated sun shield to make viewing it outdoors much easier.
If you have any other questions just let me know .