[phpexcel] PHPExcel - set cell type before writing a value in it

The same way as you'd set the type (number format mask) after writing a value to it:

$objPHPExcel->getActiveSheet()
    ->getStyle('A1')
    ->getNumberFormat()
    ->setFormatCode(
        PHPExcel_Style_NumberFormat::FORMAT_GENERAL
    );

or

$objPHPExcel->getActiveSheet()
    ->getStyle('A1')
    ->getNumberFormat()
    ->setFormatCode(
        PHPExcel_Style_NumberFormat::FORMAT_TEXT
    );

Though "Number" isn't a valid format mask.

You can find a list of pre-defined format masks in Classes/PHPExcel/Style/NumberFormat.php or set the value to any valid Excel number format masking string.