Hello,
Using phpdocx 10, please check the docs folder included in the package. phpdocx 11 renamed this folder to macros-libreoffice.
In this folder you can read the instructions and the macros to be used with the conversion plugin based on LibreOffice. To generate PDF/A-1 files, you need to add the Generate PDF A-1.txt macro to your LibreOffice installation (as explained in How to use macros.txt) and then call:
$docx->transformDocument('document.docx', 'document.pdf', 'libreoffice', array('pdfa1' => true));
We also recommend you use the latest version of LibreOffice.
Regards.