$re = '/\+31(14\d{3,5})(?=\D|$)/m';
$str = '+3120345643
+311403
+3114035
+311402431
+31140457487';
$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