<?php
use Microsoft\Graph\GraphServiceClient;
use Microsoft\Graph\Generated\Models\Security\EdiscoveryCaseMember;
use Microsoft\Graph\Generated\Models\Security\RecipientType;
$graphServiceClient = new GraphServiceClient($tokenRequestContext, $scopes);
$requestBody = new EdiscoveryCaseMember();
$requestBody->setRecipientType(new RecipientType('roleGroup'));
$requestBody->setDisplayName('Security Administrator');
$result = $graphServiceClient->security()->cases()->ediscoveryCases()->byEdiscoveryCaseId('ediscoveryCase-id')->caseMembers()->post($requestBody)->wait();