How to aply group by and order by Dynamodb factory

Question

Below scan method is working code. But I want to apply group by and order by ASC/DESC

$result = $client->scan(
        array(
            'TableName' => 'chat',
            'ProjectionExpression' => "ChatId, first_name, last_name", 
            //Select first_name, last_name
            //'KeyConditionExpression'=> 'first_name = :value1 AND first_name = 
             :value2',
            'FilterExpression' => 'first_name = :value1 OR first_name = 
            :value2 
             OR first_name = :value3',
            'ExpressionAttributeValues'=> array(':value1' => array('S' => 
              'Sunil'), ':value2' => array('S' => 'Rakesh'),  ':value3' => 
              array('S' => 'Sudhir')),
             //'ScanIndexForward' => false,
            //'Limit' => 2
            // 'TotalSegments' => 2
        )
    );