Where do you exactly want to do that?
If you want to change the text size of the Android OS, you can do that at Settings➡️Display➡️Font size and style.
That only works for general font size of everything on the phone EXCEPT texting. It does not adjust the size of the font size for texting.
How do you adjust the font size for texting?
Did you mean the keyboard size or the size of the typed text?
Yes, I meant the size of the typed text - however, I've recently found the remedy.
I should have posted back here to say same. It was remiss of me not to do so.
Thank you for your reply.