About 2 feet and that comparison is useless as it does not operate at 2.5Ghz and its not 1 inch from my brain. I'm still not sold on the WHO's conclusions but your lumping ANY kind of radiation into the mix and it's not the same.
More or less, all electromagnetic radiation IS the same stuff. The difference among the different types of the stuff is the frequency (and related energy.) There's nothing magical about 2.5 gigahertz. It's midway between 2.4 gigahertz and 2.6 gigahertz. Its energy is halfway between the energy of 2.4 gigahertz output and 2.6 gigahertz output. And, that energy is a tiny, tiny, tiny fraction of the minimum amount of energy that's necessary to affect a genetic change which would lead to cancer under ANY known mechanisms.
I'll try an analogy. Think of your genetic material as being a big armor plated tank. Visible light would be like bullets. Most of the bullets aren't capable of damaging the tank... at all. A few of the most powerful bullets actually are capable of a tiny bit of damage, but damage nonetheless. Cannonballs are more capable; these would be like ultraviolet radiation. And, big ass missiles are even more capable yet - these are like xrays and gamma rays.
Now, in this analogy, what are the waves emitted from your phone like? Well, they'd be like packing peanuts. No, wait, that's too powerful. They're like the little tiny styrofoam balls that they stuff cheap stuffed animals with. Nope, that doesn't work either, because that's still a couple orders of magnitude too powerful. I guess the best I'm going to do here is say that cell phone radiation is like having little tiny styrofoam balls that are about the size of a grain of sand. And, you've got to damage the armor coating on the tank by shooting them - at the same speed the bullets were traveling at - at the tank.
So, could you actually do some damage to the tank with them? Sure - with gadzillions of them shot all at once. This would relate to the power output of the phone though. Your cell phone is only capable of sending out a few hundred of these tiny grain sized pieces of styrofoam per second, more or less in all directions, so the the closer you are to the tank, the more are going to hit it. Still, even if you were against the tank, there's not enough total energy to do anything to it with those styrofoam grains.
Any argument about it being 2.5 gigahertz is like saying that "well, maybe a 0.000100 meter styrofoam ball isn't going to damage the tank, but how about a 0.000101 meter styrofoam ball? Or a 0.0000999 meter styrofoam ball?