The restriction on cellular phone use on a plane comes from the FCC not FAA.
As far as the FAA is concerned as long as you can demonstrate (through standard tests) that a class of aircraft is tolerant of electronic devices (which the manufacturers can do), it’s up to the airline if they want to allow it. They’ve even greatly simplified the process due to the explosion of different electronic devices over the last couple decades. This covers your cell phone in the same way it does an e reader or anything else. [0] There are basically no substantiated instances of portable electronics interfering with aircraft. Certainly not the number you’d expect given the massive number of devices that transit on a massive number of planes every day at this point.
The restriction on usage comes from the FCC, applies specifically to using land mobile frequencies from aircraft, and is not out of concern for safety of the aircraft.
Things getting up into VHF, UHF and above are “line of sight” propagation. If you can draw a straight line between two points without hitting anything that will attenuate the signal… it’ll pretty much go anywhere. Voyager 1 is transmitting 15 billion miles to us on 8GHz with a 23 watt radio. Your cell phone can put out around 3 watts. People called in to ham radio nets in Vancouver, BC from Seattle, WA on a 5W handheld radio just by going to the top of the Space Needle. People regularly make contact with the ISS or satellites on similar power. A large limiting factor to the distance is the height of the transmitter. Thanks to the curvature of the Earth, over enough distance, that straight line between the two points will begin to intersect the Earth which works great to attenuate the signals to nothing. Getting higher up lets you "shout" further out.
Your cell phone transmitting at 3 watts from that kind of altitude is potentially hitting dozens or hundreds of cell towers. Frequencies which are intended to be shared among inhabitatants in a maybe dozen mile radius now need to be shared across hundreds of miles, reducing the bandwidth available for everyone. And the weak signal will cause interference substantially further.
The FCC limited transmissions while on an aircraft to prevent interference with ground communications, and continues to because there isn’t enough evidence that they won’t.
[0] https://www.faa.gov/documentLibrary/media/Advisory_Circular/...