Radio / Telephone radio frequency radiation is non ionizing.
This means that it does not cause mutation, the only thing it does is cause heating - think microwave popcorn.
This is one of the most basic things they teach you when you actually study to get your amateur radio licenses - not the hamburger in a day type class or a cheat sheet with just the questions and the answers.
My communications background allows me to delve deeper into the subject.
The first cell phones to come out - what I call a bag phone, was an analog device that produced anywhere from 5 to 50 watts. The phone signal had to be robust because the spacing between the cell towers were at least 20 miles apart. The logic was that 2G - second generation type phones had the highest demand in places where there was the most people. So the cell phone companies - to get a jump on their competition, put up a couple of basic towers to cover a large area. With an outside the vehicle antenna, it was possible to get some coverage - which was enough to sell a whole lot of phones - which paid for the system upgrades.
By the time we got to 3G - 3rd Generation, the build out was enough that they were able to make the phones smaller, the antennas smaller, reduce the amount of transmit power.
The logic is also - if you move the cell tower closer to the user, you can use less power to complete the call.
This reduces the demand on the battery, which makes the battery last longer.
The cell tower pings the cell phone from time to time. This is just the GPS reporting where you are at.
There is no way short of taking out the battery or disabling the phone to stop the phone from reporting where you are at. This is the NSA and the FBI and the CIA and the State Polices way of looking to see who was in the area when a certain crime was committed.
As far as your phone being turned off and yet producing enough RF to cause sterilization - I highly doubt if it is possible.
I would be more worried about a person getting cancer from holding the phone next to their ear, this is probably the reason for the invention of Bluetooth and speakerphone functions.. The liability alone is going to cost billions if you could ever relate the two and get some Federal Judge to award a settlement...
This is the main reason why I do not own a cell phone and I do not use a cell phone.
Until 2 months ago, all I had was Verizon Copper - landline..
Everything you say on your cell phone for at least 5 years is being recorded and stored.
Everything you text on your cell phone for at least 5 years is being recorded and stored.
Every picture you take or share is being recorded and stored at least 5 years! Maybe 10!
Anything involving cryptology -before the designer can produce a copy, they first have to give a copy of the keys to the government. So nothing you can do - other then designing your own program is secure.
And anything you design, the government can decode it in about an hour - if they want to!
Anything you need to want to be secure must be done face to face or by using some type of radio with a limited range - since it is highly unlikely that the government is going to waste their time trying to listen to every amateur radio frequency, GMRS, FRS and MURS, this is where you probably need to start to learn about wireless communications...