<?php
use Microsoft\Graph\Beta\GraphServiceClient;
use Microsoft\Graph\Beta\Generated\Users\Item\Messages\Item\Attachments\CreateUploadSession\CreateUploadSessionPostRequestBody;
use Microsoft\Graph\Beta\Generated\Models\AttachmentItem;
use Microsoft\Graph\Beta\Generated\Models\AttachmentType;
$graphServiceClient = new GraphServiceClient($tokenRequestContext, $scopes);
$requestBody = new CreateUploadSessionPostRequestBody();
$attachmentItem = new AttachmentItem();
$attachmentItem->setAttachmentType(new AttachmentType('file'));
$attachmentItem->setName('flower');
$attachmentItem->setSize(3483322);
$requestBody->setAttachmentItem($attachmentItem);
$result = $graphServiceClient->me()->messages()->byMessageId('message-id')->attachments()->createUploadSession()->post($requestBody)->wait();