<?php
use Microsoft\Graph\Beta\GraphServiceClient;
use Microsoft\Graph\Beta\Generated\Models\WorkbookComment;
use Microsoft\Graph\Beta\Generated\Models\WorkbookCommentMention;
$graphServiceClient = new GraphServiceClient($tokenRequestContext, $scopes);
$requestBody = new WorkbookComment();
$requestBody->setCellAddress('Sheet1!A1');
$requestBody->setRichContent('<at id=\"0\">Kate Kristensen</at> - This is my comment.');
$mentionsWorkbookCommentMention1 = new WorkbookCommentMention();
$mentionsWorkbookCommentMention1->setId(0);
$mentionsWorkbookCommentMention1->setName('Kate Kristensen');
$mentionsWorkbookCommentMention1->setEmail('kakri@contoso.com');
$mentionsArray []= $mentionsWorkbookCommentMention1;
$requestBody->setMentions($mentionsArray);
$requestBody->setContentType('mention');
$result = $graphServiceClient->drives()->byDriveId('drive-id')->items()->byDriveItemId('driveItem-id')->workbook()->comments()->post($requestBody)->wait();