Have you tried increasing the font size? It may sound daft but normally the obvious is the simple answer.
Most CMS have an easy option to change the font size across the whole website and you can test it to make sure it does not have an adverse effect on larger screens.
The other point that springs to mind is to make sure you don’t have any really small text on the page, check your footer for one, but also if the domain has spammy text hidden with really small text size that won’t help.