The characters are too small to decipher? You would like to be able to read comfortably from afar?
iPhones have a general setting that allows you to adjust the font size. The following entry from Apple explains how: https://support.apple.com/en-us/HT202828
For Android smartphones, we added a “zoom in” button to enable you to enlarge the font during a call. The button is green, with a white magnifying glass and you can find it on the left of the red “hang-up” button.
Press it to zoom in and enlarge the font.