$re = '/.*(7\d{6}).*/';
$str = 'aksjhaksghlkas NSLsf
sklvbaskjhbvak vjadv 09,00mm
123456416584 7001122 asvljalskjfg 564563
34893 ajksha';
$subst = "$1";
$result = preg_replace($re, $subst, $str);
echo "The result of the substitution is ".$result;
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