Donations page on mobile phone not formatting properly on Wordpress site
The public-facing donation and event pages inherit their look and feel from the Wordpress theme.  If there's overlapping text, it can't be fixed within CiviCRM; it must be fixed within WordPress.  You should be able to confirm this by loading a Wordpress default theme like twentyseventeen on your site (ideally a test version of your site), and the problem shouldn't exist.

As for which part of the theme needs fixing, it's very hard to troubleshoot without seeing the CSS of the page itself, which means posting the URL in question.  That said - you'll likely get better answers in the Wordpress Stack Exchange than here.