It was still pretty out there. RF in these frequencies isn’t new. Radar installations have been using them for decades before, and at far higher power levels than what comes out of any cell phone.
Not only that, but today’s cell phones tend to use less output power than those old bricks from the '80s. If there were issues, we’d expect early adopters to be affected all the more, and there just wasn’t anything there.
Could there be a difference in how the signal works between radar, analog phones, and digital phones that causes a problem? If it had, it would have been a big surprise. Still, there was a crack of possibility open, which is now sealed shut.
WHO uses the precautionary principle a little too hard sometimes. If it was carcinogenic at all, it’d be at a very small rate.