Some iPhones have built-in apps https://pokiapp.com/movie-hd-for-android/ for streaming 4K content, such as Netflix. In addition, you can download the apps from the iTunes Store to your device. You can then view them on the Apple TV app.
The main benefit of downloading the app is that you’ll have access to a huge library of content at any time. You can also stream movies on your FireStick or Android TV.