it must be the form you are sending it from. show us the code you are using to send it.
i re-created it here:
http://codenewbie.com/test.php
Here is the code:
PHP Code:
<?
$_POST[DisplayPhone] = "9876543210";
if(($_POST[DisplayPhone] == 0) OR ($_POST[DisplayPhone] == "") OR is_null($_POST[DisplayPhone]))
{
echo "true";
}
else
{
echo "false";
}
?>