You should still set airplane mode when airborne for other reasons besides interference with the aircraft. For one, you’ll save your battery. It takes a lot of “juice” for your device to search for cell towers that are likely out of reach. You may also want to avoid connecting to a tower outside where you have coverage. E.g. for a flight from Anchorage to Minneapolis, maybe you don’t want to connect to Canadian cell towers and potentially receive charges in another country. Obviously this depends on your plan limits. But, yeah, it’s not really about protecting the airplane, in most cases