I'm assuming you've made the common mistake of writting your php code within your webpage file, or trying to put the meta-tag within the php code.
*I'm no pro w/ php, but this one i have covered
Instead use a standard start and include the meta tag as you would in any html file. This would allow you to write the meta tag individually for each page, then use an include
statement to add your header/footer files to it as well. (eg: include( 'header.php' ); )
*Although there is nothing technically wrong with not doing it this way, it is more 'proper' as far as programming style