Since there are still regulations on safe limits, probably that’s true. To be honest I don’t know what I believe, but I stay on the safe side.
However I understand that back in the days people didn’t need or use their phones as often as now. Phones or even computers had one place where they were stationed, and their signal was relatively stable and not like nowadays when phones connect to various cellular towers.
To me, cellular connections are completely useless to be on for full 24 hours, not only they are the ones responsible for “heat tissue” side effects, but also they drain battery. It was ok when we all had Nokias and poor, expensive cellular internet and lack of decent instant messaging apps.
Nowadays we are surrounded by FaceTime, iMessage, WhatsApp, Telegram and so on, i.e. apps that work on wifi much better than on any cellular.
So while turning off phone at night can be overkill, it is worth to put phone on airplane mode to disable cellular module - useless battery drain and additional, unneeded RF exposure