Hi,
yes, you can do that either using the Custom Fields extension https://wpadverts.com/extensions/custom-fields/ or by adding the code below in your theme functions.php file (or even better by creating a new blank plugin and pasting it there https://wpadverts.com/blog/how-to-use-code-snippets-in-wordpress/).
add_filter( "adverts_form_load", function( $form ) {
if( $form['name'] != "advert" ) {
return $form;
}
foreach( $form["field"] as $key => $field ) {
if( in_array( $field["name"], ["adverts_phone", "advert_category"] ) ) {
$form["field"][$key]["validator"][] = ["name"=>"is_required"];
}
}
return $form;
} );