Excel stores dates/times as the number of days since 1st January 1900 (or 1st January 1904 if your workbook uses the Mac 1904 calendar). This is why the cell value is 40451... that's it's value in Excel, and in PHPExcel. The only thing that differentiates
this from any other number is the formatting mask applied to the cell.
You can identify if a cell contains a date using:
which will return a boolean true if cell A1 contains a value that is formatted as a date.
To read the cell value as a PHP date, you can use the date conversion functions:
$phpDate = PHPExcel_Shared_Date::ExcelToPHP($objPHPExcel->getActiveSheet()->getCell('A1'));
to convert an Excel/PHPExcel date to a PHP date/timestamp, and then use standard PHP date() function for formatting
Alternatively, to read the cell value as a formatted string,
$dateString = PHPExcel_Style_NumberFormat::toFormattedString($objPHPExcel->getActiveSheet()->getCell('A1'), 'MM-DD-YYYY');