Fun fact: many pilots actively use ipads, phones, and bluetooth headsets in the cockpit with all the radios on throughout the flight. Wifi too. Turning the ipads in the cockpit off or in airplane mode is not on any checklist of any plane. Better still they actually get mounted on or near the yoke so the pilot can look at it and use it while they are flying.

They are an indispensable tool for situational awareness, navigation, and even as backup instruments (though non certified of course). Pilots will even bring them to exams and instructors and examiners are not against that and they are about as normal as paper maps used to be. Modern navigation equipment (e.g. the Garmin's G1000) also can pair with an ipad and accept input from it or sync with it. A phone is a great thing to have when the tower isn't responding because the person is taking a break, or it's after hours, or you have some kind of radio failure. You can talk to flight control over a phone from inside the cockpit of a plane to get your clearance too. It's not illegal or frowned upon.

This includes many airliners btw. And the FAA has long approved using ipads and many commercial airlines use them routinely. So, bluetooth and wifi are both used in cockpits. Any modern airliner is completely resilient against that and would have been hardened a long time ago. Any equipment at all sensitive to radio frequencies used by consumer equipment would have a hard time getting certified at this point.

So, the obsession with the little pocket radios (phones, kindles, etc.) that airlines have is kind of silly at this point. Especially since it's limited to takeoffs and landings on most flights and nobody actively checks any of this other than to police people to remove their head sets randomly (about 1 in 5 times I get told off). Stewardesses using equipment to detect the 50% of the passengers that don't bother with or forget about turning their radios off is not and has never been a thing. That's because it's a complete waste of time and it doesn't matter one bit from a safety point of view. If that wasn't the case, there would be hefty fines on this. There aren't.

A valid reason to turn devices into flight safe mode anyway is simply to save a bit of battery. Phones will eat up a lot of battery trying to reach base stations that aren't there or that are passing by to quickly to keep up with.

That being said, some airlines offer 4G connectivity in flight. Obviously, you'd have to turn your phone radio on to make use of that. With 5G and things like space link, I imagine in flight connectivity is only going to become only more common.