<?php
use Microsoft\Graph\GraphServiceClient;
use Microsoft\Graph\Generated\Users\Item\MailFolders\Item\ChildFolders\ChildFoldersRequestBuilderGetRequestConfiguration;
$graphServiceClient = new GraphServiceClient($tokenRequestContext, $scopes);
$requestConfiguration = new ChildFoldersRequestBuilderGetRequestConfiguration();
$queryParameters = ChildFoldersRequestBuilderGetRequestConfiguration::createQueryParameters();
$queryParameters->includeHiddenFolders = "true";
$requestConfiguration->queryParameters = $queryParameters;
$result = $graphServiceClient->me()->mailFolders()->byMailFolderId('mailFolder-id')->childFolders()->get($requestConfiguration)->wait();