As Mitina said, we set our iPhones to airplane mode the minute we get on the plane and leave them like that for most of the trip.
Your phone can still use Wi-Fi while in airplane mode. So when we get onboard or to our hotel, we connect to Wi-Fi, always without turning off airplane mode.
The only time we turn off airplane mode is when we need to use the phone while on land and away from Wi-Fi. We use Verizon’s $10/day TravelPass for that.
Airplane mode will protect you from unwanted charges!
Caveat: if you want to make calls, make sure your phone’s settings are set to allow calls over WiFi. I don’t know how to do this on Android phones; probably Google can tell you. On an iPhone, go to Settings > Phone > Wi-Fi Calling.