Nobody could do a better job presenting this issue and how it came to be than Joel Moskowitz, Ph.D., at the UC Berkeley School of Public Health.
https://www.saferemr.com/2017/03/cell-phone-safety-guidance-from.html
Here is the link to the CDPH document advising on cell phone use and reducing EMF exposure.
https://www.cdph.ca.gov/Programs/CCDPHP/DEODC/EHIB/CDPH%20Document%20Library/Cell-Phone-Guidance.pdf