Hi,
It would probably be correct to assume that your model is listed in About AirPrint - Apple Support. The printer and the iPhone must be connected to the same network (Wi-Fi router). If so, you could try the following procedure:
Power off the Wi-Fi router, the printer, the iPhone, and all other devices/computers. Wait two to three minutes. Power on the router. Wait two to three minutes. Power on the printer. Wait a minute or two. Power on the iPhone. Finally, power on all other devices/computers.