Airplay data usage
I have a mobile cellular router at my cottage with limited data.
i also have a smart tv with Apple TV.
if I AirPlay video that is stored on my phone to the tv, will it use any of my data?
AirPlay video requires the iPhone and Apple TV to be on the same Wi-Fi network. Will it use that data? Yes, and plenty of it.
Use AirPlay to stream video or mirror the screen of your iPhone, iPad, or iPod touch - Apple Support