Hello,
The Premium package includes the following samples that set legendPos as 'none': sample_2.php and sample_16.php.
It seems your code is seting legendPos as 'none', so no legend tag is created, and you are trying to set a legend style using the legendArea option. You can't apply a legend style as the legend tag doesn't exist, so phpdocx returns a not found DOM exception.
To hide elements in charts please check the show* options available in the addChart method.
Regards.