$ cat test.php 
<?php

require_once 'scripts/init/init-script.php';

$conn = id(new PhabricatorUser())->establishConnection('r');

$query = qsprintf(
  $conn,
  'SELECT %P',
  new PhutilOpaqueEnvelope('hunter2'));

echo $query."\n";
var_dump(queryfx_one($conn, '%Q', $query));

$ php -f test.php 
SELECT ********
array(1) {
  ["hunter2"]=>
  string(7) "hunter2"
}