I noted in the comments on a previous post that after my mom died from brain cancer, I now make a habit of only talking on my phone in "speaker mode" or else using a wired headset. I also don't keep the phone on my person when I don't have to. I typically keep it on a nearby table or shelf. I just don't want the phone transmitting in close proximity to my body, especially my brain, any more than necessary.

Beyond that, I don't worry about it too much, because the signal strength falls off very quickly as distance increases. But I always try to read new articles on the subject, just so I'm aware of the current state of knowledge.