<?php
use Microsoft\Graph\GraphServiceClient;
use Microsoft\Graph\Generated\Communications\Calls\Item\Answer\AnswerPostRequestBody;
use Microsoft\Graph\Generated\Models\Modality;
use Microsoft\Graph\Generated\Models\ServiceHostedMediaConfig;
use Microsoft\Graph\Generated\Models\MediaInfo;
$graphServiceClient = new GraphServiceClient($tokenRequestContext, $scopes);
$requestBody = new AnswerPostRequestBody();
$requestBody->setCallbackUri('https://bot.contoso.com/api/calls');
$requestBody->setAcceptedModalities([new Modality('audio'), ]);
$mediaConfig = new ServiceHostedMediaConfig();
$mediaConfig->setOdataType('#microsoft.graph.serviceHostedMediaConfig');
$preFetchMediaMediaInfo1 = new MediaInfo();
$preFetchMediaMediaInfo1->setUri('https://cdn.contoso.com/beep.wav');
$preFetchMediaMediaInfo1->setResourceId('1D6DE2D4-CD51-4309-8DAA-70768651088E');
$preFetchMediaArray []= $preFetchMediaMediaInfo1;
$preFetchMediaMediaInfo2 = new MediaInfo();
$preFetchMediaMediaInfo2->setUri('https://cdn.contoso.com/cool.wav');
$preFetchMediaMediaInfo2->setResourceId('1D6DE2D4-CD51-4309-8DAA-70768651088F');
$preFetchMediaArray []= $preFetchMediaMediaInfo2;
$mediaConfig->setPreFetchMedia($preFetchMediaArray);
$requestBody->setMediaConfig($mediaConfig);
$graphServiceClient->communications()->calls()->byCallId('call-id')->answer()->post($requestBody)->wait();