turning off location only prevents some installed apps from accessing it, but your mobile provider still knows where you are (even if you’re on a VPN and websites think you’re in Amsterdam) and Apple & Google know your constant location on iPhones and androids no doubt. I would be extremely skeptical of Airplane mode on these devices because who knows? Best way to prevent smartphone from phoning home is a modification like this printer got https://m.youtube.com/watch?v=N9wsjroVlu8