Hello,
There's no method or option to get the numbering value of a list item, as it's set dinamically when the DOCX is open. Maybe you could use addLink with an internal bookmark (https://www.phpdocx.com/api-documentation/word-content/insert-link-Word-document-with-PHP), adding a fixed string. But to change a bookmark value of a link dinamically you may need to use DOCXCustomizer (https://www.phpdocx.com/documentation/introduction/docxcustomizer) that is only available in Premium licenses.
Regards.