PHPOffice/PHPPresentation (PowerPoint) Chart (createChartShape) how to access and change font size and color of axis labels?

Question

In PHPOffice/PHPPresentation chart shape I need to change color and font size of labels on X and Y axis like for example here:

https://jsfiddle.net/462gxdn3/

xAxis->labels->style->color:'#0000FF'
xAxis->labels->style->fontSize: 15

This changes font color and size of X axis labels.

What I've tried in PHPPresentation:

$oShape = $currentSlide->createChartShape(); // ..etc. and chart looks good
$oShape->getPlotArea()->getAxisX()->getFont()->setSize(7);

But the second line does nothing. Labels font size remains unchanged. Do you know how font properties of axis labels can be accessed?