<?php
 
$string = 'Texto de teste <i class="fab fa-accusoft">xxx</i> Teste Lorem Ipsim <i class="fab fa-accusoft">xxx</i>';
$doc = new DOMDocument();
$doc->loadHTML($string, LIBXML_HTML_NOIMPLIED|LIBXML_HTML_NODEFDTD);
 
$selector = new DOMXPath($doc);
foreach($selector->query('//i[contains(attribute::class, "fa-")]') as $e){
    $e->parentNode->removeChild($e);
}
 
$string = trim(preg_replace('/<p>|<\/p>/', '', str_replace('  ', ' ', $doc->saveHTML())));
 
echo $string;

PD9waHAKCiRzdHJpbmcgPSAnVGV4dG8gZGUgdGVzdGUgPGkgY2xhc3M9ImZhYiBmYS1hY2N1c29mdCI+eHh4PC9pPiBUZXN0ZSBMb3JlbSBJcHNpbSA8aSBjbGFzcz0iZmFiIGZhLWFjY3Vzb2Z0Ij54eHg8L2k+JzsKJGRvYyA9IG5ldyBET01Eb2N1bWVudCgpOwokZG9jLT5sb2FkSFRNTCgkc3RyaW5nLCBMSUJYTUxfSFRNTF9OT0lNUExJRUR8TElCWE1MX0hUTUxfTk9ERUZEVEQpOwoKJHNlbGVjdG9yID0gbmV3IERPTVhQYXRoKCRkb2MpOwpmb3JlYWNoKCRzZWxlY3Rvci0+cXVlcnkoJy8vaVtjb250YWlucyhhdHRyaWJ1dGU6OmNsYXNzLCAiZmEtIildJykgYXMgJGUpewogICAgJGUtPnBhcmVudE5vZGUtPnJlbW92ZUNoaWxkKCRlKTsKfQoKJHN0cmluZyA9IHRyaW0ocHJlZ19yZXBsYWNlKCcvPHA+fDxcL3A+LycsICcnLCBzdHJfcmVwbGFjZSgnICAnLCAnICcsICRkb2MtPnNhdmVIVE1MKCkpKSk7CgplY2hvICRzdHJpbmc7