The example demonstrates how to retrieve and filter items by Managed Metadata field (column) value

filterByMM.php

<?php

require_once './vendor/autoload.php';
$settings = include('./settings.php');

use Office365\Runtime\Auth\ClientCredential;
use Office365\SharePoint\CamlQuery;
use Office365\SharePoint\ClientContext;


$credentials = new ClientCredential($settings['ClientId'], $settings['ClientSecret']);
$siteUrl = $settings['TeamSiteUrl'];


/**
 * The example demonstrates how to retrieve and filter items by Managed Metadata field (column)
 * Three options are considered:
 *   1) filter with OData filter query option
 *   2) filter with CAML query  <-- note: recommended and tested on my env
 *   3) client side filtering
 */


$ctx = (new ClientContext($siteUrl))->withCredentials($credentials);
$listTitle = "Documents";
$list = $ctx->getWeb()->getLists()->getByTitle($listTitle);

//Option 1: filter with OData filter query option
//As we discussed: this option will NOT work since filtering by managed metadata is not supported by OData in SharePoint API
//The next line will throw the exception
//$items =   $list->getItems()->filter("Module eq 'Finland'")->get()->executeQuery();

//Option 2: filter with CAML query
//This approach should work as expected. We utilize CAML query which supports filtering by Managed Metadata field
//

$qry = new CamlQuery();
$qry->ViewXml = <<<XML
<View Scope='RecursiveAll'>
    <Query><Where><Eq><FieldRef Name="Module" /><Value Type="TaxonomyFieldType">Finland</Value></Eq></Where></Query>
    <RowLimit Paged="TRUE">1000</RowLimit>
</View>
XML;
$items = $list->getItems($qry)->executeQuery();


/**
 * Managed Metadata field value is represented as array in the following format:
 *  {
       Label="Finland"
       TermGuid="--guid goes here--"
       WssId=-1
     }
 */
foreach ($items as $item){
    print($item->getProperty("Module")["Label"] . "\r\n");  //print label
}


//Option 3: filter with CAML query
//I would suggest to utilize option 2 instead :)