But these studies were done when phone were used excessively for calls, which is probably not the case today.
EMF radiation is one of those areas which probably need much more research.
Simple answer, we're not sure.
now its harmfulness is in levels, the higher freq. is, ie. higher G, the higher the harmfulness is
some believe there's some improvement in its mitigation by H/W design, but most think that can only do little
all we should do is: must absolutely have routine scheduled to go to open clean nature space some hours in a day or week
just google the detailed correctness in applying it completely
https://news.ycombinator.com/item?id=30862227
Further search also shows up a metric shedload of usual conspiracy theory stuff, so be aware of that.