How can I completely block the phone from being able to call 911. My son figured out the 5 clicks on a deactivated/no sim cell phone and he keeps calling 911. I want him not be able to.
Welcome to Apple Support Communities. We understand that you would like to prevent accidental calls to emergency services.
While completing blocking 911 calling isn't a current option, you can turn off features such as Auto Call and Call with Side Button which will prevent these calls. Check out Use Emergency SOS on your iPhone for details.