That would take an hour and a half to heat an adult brain up by 1 Kelvin,
That's an oversimplification assuming the entire brain receives the exact same amount of energy, and that is just the radio transmissions, while a cell phone can also output heat on its own and reflect your body heat.
These "Platonic thought experiment" rebuttals tend to be simplistic to the point of "assuming spherical cows" and ignore the complex interactions of a real biological system. That's not a valid scientific argument, at best it's a plausibility argument.
We didn't think asbestos was a carcinogen but it was. We then thought glass fibers were likely to be carcinogens too, but they weren't.
That's the same amount of 'heating' as 45 minutes of cell phone use, every day.
Any cell phone use comes on top of all that, and some professions could easily spend more than an hour a day on the cell phone. (Though admittedly they'd normally get a hand-free set then.)
It's not enough to come up with some vague correlation if every other verified theory tells us that it just can't happen. A mechanism for the cause has to be proposed (a model), and it has to be shown to be valid rigorously, using double-blind studies and falsifiable experiments.
A correlation can be plenty to work with if you can clearly prove it. If the correlation can not be explained by other established models, or discarded as coincidence, you can then start searching for a underlying mechanism.
John Snow found a correlation between drinking from a certain well and outbreaks of cholera. The mechanism of infection was not known at the time, but even so the correlation was clear and undeniable.
The problem here is rather that they have tested for a correlation and there isn't one. Empirically testing a hypothesis you don't like is not pseudo-science.