<?php
use Microsoft\Graph\GraphServiceClient;
use Microsoft\Graph\Generated\Chats\Item\ChatItemRequestBuilderGetRequestConfiguration;
$graphServiceClient = new GraphServiceClient($tokenRequestContext, $scopes);
$requestConfiguration = new ChatItemRequestBuilderGetRequestConfiguration();
$queryParameters = ChatItemRequestBuilderGetRequestConfiguration::createQueryParameters();
$queryParameters->expand = ["lastMessagePreview"];
$requestConfiguration->queryParameters = $queryParameters;
$result = $graphServiceClient->chats()->byChatId('chat-id')->get($requestConfiguration)->wait();