How to set font size 12 on php printer

Question

Good day guys, I need your help to fix my code. Im using client's printer and I need to set the font to 12 because the output is to large. please check the code below

    $content .= "This receipt is for inventory purpose only.**";
$printer = ("MYPOS");
$handler = printer_open($printer);
if ($handler) {
    printer_write($handler, $content);
    printer_close($handler);
} else {
    echo "not connected";
}