Good info.

nokia flip phone?

Put phone in airplane mode when at home or somewhere with WiFi, since WiFi is a lot lower power than cell transmissions. And know that those stupid radiation-reduction sleeves have the opposite effect since the phone detects the weakened signal and increases its transmit power to compensate.

If you’re worried about potential health consequences, using a Bluetooth headset

Yeah, put a transmitter right in your ears. No, use speakerphone.