Always put the phone on speakerphone and keep it away from your head.

This is no longer a fringe conspiracy theorist thing (though research on it is still early and relatively sparse).

For example:

https://edition.cnn.com/2018/05/02/health/brain-tumors-cell-...

https://pmc.ncbi.nlm.nih.gov/articles/PMC5417432/

Maybe it is causing certain cancers, maybe it isn't. Science will probably know more in 10 years. But in the mean time, why take on unnecessary risk?