The controversy continues about whether or not intensive cellphone use can cause brain damage. Some neurosurgeons make a point of only using their mobiles in speakerphone mode. That’s fine if you don’t want a private conversation.
If you do (and frankly I’d prefer medics to take privacy more seriously) then consider today’s invention.
It’s an ear trumpet/speaking tube for the modern era.
As shown, this is in the shape of a tube, just flexible enough to be slung around the neck and yet with an internal coating which provides for effective in-tube sound transmission. This scarf-like device allows a cellphone to be inserted securely: another answer to the question of how to carry one of these things around.
The phone’s speaker and mic. would each be in communication with half of the tube: an internal wall dividing these two sections. This would allow someone to speak and listen without holding the aerial near their cortical cells.