The pheonix is not that large and lays no egg, but is reborn from fire--according to the stories, anyway. A dragon is bad, unless it is intelligent and reasonable enough not to attack.

It could be a roc's egg, I suppose. They were described as eagles large enough to carry away elephants, and that sounds about right. *He taps at the egg for a moment.* Interesting. I daresay that if you could tame whatever lays these eggs, world hunger would be given a serious blow.