Hello,
Using getWordStyles (https://www.phpdocx.com/api-documentation/docx-path/get-styles-word-contents-in-docx) you can return the styles applied to specific contents. Please note that Word applies cascade styles (default styles, custom styles, inline styles)
On https://www.phpdocx.com/documentation/snippets/get-font-size-content you can read a sample that returns the font size of a content.
Regards.