Have not read through all the comments, and probably won't, so perhaps this has already been pointed out.
I don't see that my phone is any more at risk than my hands, I can wipe the desk down with a sterilizing wipe, and do the same with my phone if I want. I tend to keep my phone either in my hand or in a pocket when outside my house. So as far as I can see the phone is not more a threat than my hands.
However, I is not uncommon for me to have my phone touching or very near my face, ears, mouth.
Has anyone suggested using speaker and holding the phone away from your face? Or is the assumption that everyone just used wired or bluetooth headsets/earbuds with a mic?