Speaking through the phone will sometime result is having to speak clearly for the caller

Speaking through the phone will sometime result is having to speak clearly for the caller. For example if they are stressed and worried, obviously you would need to give them more time to speak and get all their concerns across. It would also result in having to speak slowly and with a calmer tone of voice. So they believe that you are trying to reassure and help them.
When talking to different audience groups you need to speak in a way which they will all understand. The older generation may prefer to send letters instead of emails. Which may result in having to make the font larger as they may have a sight impairment. And will not be able to read it if it was too small.