Fixed the issue here it was as Mark Baker said, so my code now looks like this:
Include_once 'PHP/PHPExcel.php';
$objPHPExcel = new PHPExcel();
$activeSheet = $objPHPExcel->getActiveSheet();
$objPHPExcel->getActiveSheet()->setTitle('Senior Managers Site Tour');
$objPHPExcel->getActiveSheet()->getColumnDimension('A')->setWidth(77);
$styleArray = array(
'borders' => array(
'allborders' => array(
'style' => PHPExcel_Style_Border::BORDER_THIN
)
)
);
$objPHPExcel->getActiveSheet()->getStyle('A5:D7')->applyFromArray($styleArray);
unset($styleArray);
$objPHPExcel->getActiveSheet()->mergeCells('C6:D6');
$objPHPExcel->getActiveSheet()->mergeCells('C7:D7');