<?php
use Microsoft\Graph\GraphServiceClient;
use Microsoft\Graph\Generated\Models\VirtualEventPresenter;
use Microsoft\Graph\Generated\Models\CommunicationsGuestIdentity;
$graphServiceClient = new GraphServiceClient($tokenRequestContext, $scopes);
$requestBody = new VirtualEventPresenter();
$identity = new CommunicationsGuestIdentity();
$identity->setOdataType('#microsoft.graph.communicationsGuestIdentity');
$identity->setDisplayName('Guest Speaker');
$identity->setEmail('guest.speaker@fabrikam.com');
$requestBody->setIdentity($identity);
$result = $graphServiceClient->solutions()->virtualEvents()->webinars()->byVirtualEventWebinarId('virtualEventWebinar-id')->presenters()->post($requestBody)->wait();