Hello,
phpdocx generates a HTML file after transforming the DOCX, so you just need to load this HTML in the WYSIWYG you're using.
For example, if you use CKEditor (http://ckeditor.com), you just need to create a textarea, set the CKEditor to this textare and load the HTML into it. We recommend you to check the documentation of the WYSIWYG you use.
Regards.