As a general rule, we suggest that you keep your phone at least four feet away from your bed when you sleep.
The more you can limit your exposure to EMFs, the better. This goes for tablets and computers as well.
Distance is one of the greatest forms of protection for EMF radiation emissions. According to basic principles of physics, as distance from a source of EMF radiation increases, intensity of exposure decreases dramatically; in other words, simply putting your phone a few feet away will considerably reduce the amount of EMF radiation reaching your body.
For more information on the ways EMFs affect your sleep and how to minimize the effects, please read this article.