Hello,
The next version of phpdocx will add support to change titles, categories, series... (the current version only allows to replace existing data values) using the replaceChartData method; but not to add new data points.
Just as a workaround, if you use placeholders (or unique strings) as categories and other values, this method:
http://www.phpdocx.com/api-documentation/docxutilities/raw-search-and-replace-docx
allows to replace strings in any XML of the DOCX.
Regards.