This is a good question and one that comes up a lot as we are all using our mobile phones more and more every day and keeping them close at night.
Mobile phones emit energy as radio waves which can be absorbed by the tissue in our bodies. However, this type of energy is called “non-ionising” energy, and the only known effect on our bodies is heating. This is why your ear and face might become warm during a long phone call, but not if the phone is plugged in next to your bed. “Ionising energy”, such as X-rays and radiation therapy, are linked with increased cancer risk, but this is NOT the type of energy emitted by our phones.
To cause cancer, our phones would have to damage our DNA in some way, and the type of energy they emit simply does not do that.
So, if you are worried about cancer, it is perfectly safe to use phones and to keep them near you at night.