That’s because that’s an SQL function, not PHP. You can use PDO::lastInsertId()
.
Like:
$stmt = $db->prepare("...");
$stmt->execute();
$id = $db->lastInsertId();
If you want to do it with SQL instead of the PDO API, you would do it like a normal select query:
$stmt = $db->query("SELECT LAST_INSERT_ID()");
$lastId = $stmt->fetchColumn();