To hide certain columns on the List page you need to add code to BeforeDisplay event. For instance, if column name is CustomerID use the following code. It will work in both horizontal and vertical modes.
Starting with PHPRunner 8.1 you can use the following:
$pageObject->hideField("CustomerID");
In older versions you can use the following:
$xt->assign("CustomerID_fieldheadercolumn", false);
$xt->assign("CustomerID_fieldcolumn", false);