Hello,
The default behaviour of MS Word is autofit table widths. You can set column widths but if the content of a cell doesn't fit a width then MS Word increase it width automatically.
You can force column widths setting tableLayout as fixed:
$tblConfig = array(
'border' => 'single',
'cellMargin' => 125,
'tableStyle' => 'TableGridPHPDOCX',
'tableAlign' => 'center',
'columnWidths' => array(1000,1000,1000),
'textProperties' => array('font' => 'Arial', 'fontSize' => 10),
'tableLayout' => 'fixed',
);
$docx->addTable($tblRows, $tblConfig);
This option is explained on the addTable API page:
https://www.phpdocx.com/api-documentation/word-content/add-table-Word-document-with-PHP
Regards.