You can listen to FM radio on a phone without an active data connection, but only if your phone has an activated FM chip, and only with the right app.
Unlock the Hidden FM Tuner in Your Android Phone (CNET How To)
Enabling FM Radio on an iPhone
Listen to FM Radio On Your iPhone or Android: A How-To Guide – Radio Fidelity
RadioJunction- A FREE FM Radio Online App to Listen your Favorite Radio Stations right on your Device by out thinking limited
How to use the FM radio on your Android phone
PIONEER SPH-C19BT SINGLE DIN CAR STEREO FM SMART PHONE RECIEVER/Android/ Iphone/ USB/BT/AUX/Radio at Rs 7400, Pioneer Car Audio System in Kolkata
FM Transmitter FM Radio Calling Wireless Radio 3.5mm Jack Adapter for iPhone IOS Android Car Speaker Doosl - AliExpress
How to Unlock FM Radio on Your Smartphone
Simple Radio – Live AM FM App on the App Store
REAKOSOUND Car Stereo Radio 10.1'' Carplay Universal Car Multimedia Player with BT FM Radio Receiver Support Rear View Camera
IYING Android Single Din Car Stereo Wireless CarPlay Android Auto 8 Core 2G+32G Detachable 10 Inch Touch Screen Car Radio Bluetooth AM FM GPS Navigation WiFi Car Audio Receiver with Backup
FCC asks Apple to activate the iPhone's hidden FM radio to aid public safety - The Verge
Hope FM – Our Community – Your Radio Station