Hello,
The current version of phpdocx doesn't include any method to get the WordML of existing contents in DOCX; it will be added in a next version of the library. It's a complex task due to interal dependencies and references .
Maybe you could use this method:
http://www.phpdocx.com/api-documentation/templates/replace-variable-external-file-Word-document
that allows to replace a placeholder by a DOCX, HTML, RTF or MHT. It only works for MS Word 2007 and newer.
Regards.