$re = '/(?:\b(?:tlf|mobile?|tel(?:ephone)?)[.:\s]+)?(?:\(\+45\)|\+45)?\s*\d{2}(?:\s?\d{2}){3}(?!\d)/m';
$str = 'lkdjkljlkaf tel.: +45 09827374, +45 89895867, some kind of text...
mobil: +45 20802020, +45 20802001,
afsdfadsf tlf.: +45 5555 1212
tlf: +4567890202Girrafe';
preg_match_all($re, $str, $matches, PREG_SET_ORDER, 0);
// Print the entire match result
var_dump($matches);
Please keep in mind that these code samples are automatically generated and are not guaranteed to work. If you find any syntax errors, feel free to submit a bug report. For a full regex reference for PHP, please visit: http://php.net/manual/en/ref.pcre.php