Video stream over RF and converting to Wifi
You have not stated a distance for the transmission.

WiFi is a form of RF signal, but based on what you are stating in your question, I think you meant that you want to send this video feed further than WiFi. You have a couple of options here. You could find a camera and an RF transmitter (obviously, one that has enough bandwidth and a transmission distance way further than what WiFi can reach) that can be connected to a microcontroller. Then on the receiving side, it's just a matter of picking up the transmitted signal and decoding it to be viewed to a phone.