Take the battery out.
Haow about a wee Faraday cage?
I keep mine off in the car, unless I need to make an emergency outgoing call. I turn it on at home to check for missed calls and battery strength.
“...Take the battery out...”
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No can do w/ iphone...
“Take the battery out.”
Better yet don’t own a phone of any kind. That avoids records about you. Borrow the use of somebody elses cellular or landline phone, when needed.
Or just don’t use phones. It is all voluntary.
Same applies for computers, the interwebs, credit cards, etc.
Just live under a bridge, walk to work, or don’t work.