Get DDD in (11) with regex

You can use the expression ^\((\d{2})\)

Explaining:

• ^ - Corresponds to the beginning of a string without consuming any characters.
• \( and \) - Escape is required to be treated as text and not as a set.
• (\d{2}) - Capture and group the DDD.

See PHP Live Regex

Code

$Telefone = '(11) 9.9999-9999';
preg_match("/^\((\d{2})\)/", $Telefone, $Saida);
print_r($Saida);

Exit

Array
(
    [0] => (11)
    [1] => 11
)

See working at eval.in

The response from @NoobSaibot is very good, but I'd like to leave a variation where you get the same result using preg_split with a different Regular Expression.

<?php
$string = "(11) 9.9999-9999";
$ddd = preg_split("/\(|\)/", $string);
echo $ddd[1]; // retorna 11
?>

Explanation of regex:

\( -> abre parênteses
|  -> "ou"
\) -> fecha parênteses

This will break the array string by the two parentheses (opening and closing), resulting in:

Array
(
   [0] => ""
   [1] => "11"
   [2] => " 9.9999-9999"
)

Try Ideone