mb_convert_encoding($str, "UTF-8") makes the degree symbol disapear Flickr side. I've had a look at the curl post in phpflickr now as well and it doesn't seem to send with any encoding. If I add:
curl_setopt($curl, CURLOPT_ENCODING, 'UTF-8');
it doesn't change and if I add:
$headers = array("Content-type: text/html; charset=utf-8");
curl_setopt($curl, CURLOPT_HTTPHEADER, $headers);
the durl post fails.
So much for a "small quick question".