You should be able to listen to some NFL games using the iHeartRadio app, however if you want the best iPhone radio app for finding and streaming NFL games live, I'd recommend downloading the TuneIn Radio app.
Using the TuneIn app, you can do a search for your favorite football team, and you'll see a list of stations streaming the games live. Overall, TuneIn Radio app is a bit better than the iHeartRadio app.