- preg_replace: documentation ( source)
<?php
$string = '<a href="link.html">text</a>';
echo preg_replace('/<a[^>]*>\K[^<]*/', '', $string);
echo "\n---\n";
$dom = new DOMDocument;
$dom->loadHTML($string, LIBXML_HTML_NOIMPLIED | LIBXML_HTML_NODEFDTD); // 2nd params to remove DOCTYPE);
$dom->getElementsByTagName('a')[0]->nodeValue = '';
echo $dom->saveHTML();