Hello,
The importStyles method works fine. The most common issue when working with this method is to set a wrong style name.
We recommend you to use the parseStyles method:
to get all the styles available in a document, and check that the styles are correctly created when you generate the DOCX. Also please run the included example to check if the method is running fine on your OS.
If you still have issues after following these steps, please send to contact[at]phpdocx.com the DOCX you're importing and we'll check it.
Regards.