There are Two Types of Creature on this Card Game

{Spoiler}At the very least, I would've put this at , though even then it'd be quite pushed, but close to a Plumeveil. I do think Plumeveil could be arguably considered stronger though your card has protections and more toughness (but in fairness though protections are often something that can be ignored without too much issue), but the standard otherwise for 3 mana defenders seems to be 0/X walls with a pretty mild ability. The closest example after Plumveil I could find was Guardians of Oboro, which granted for a 3/4 defender can become a regular 3/4.

So all in all, a pretty good card just maybe ever so slightly undercosted.

{Spoiler}I see what you're going for, but if you look at rare phoenixes this kind of effect almost always returns the creature to the hand. I could see this being a Bloodfeather Phoenix, but it should be noted that one has a downside, doesn't have haste by default, requires you spend resources and has a mana cost, plus besides being a bird it doesn't do anything other than reviving. I don't think it would have been a problem mechanically or flavor-wise to return this to the hand instead of the battlefield, so that's probably what you should have gone for, in my view.

I want to say though, I love that this a punishing opponents for getting more advantage type of card. I think that fits very well with the sphinx and adds more strategy to the game in a fun way. Being tied to such a condition you don't have control over could even have been a way to deal with all the matters I discussed above, but as it happens because of the last ability this card actually let's you control it. Not only that, but that second ability can (if you have no cards in hand) be turned into card advantage. More than once per turn, on any turn. On a card that will often be completely unreachable unless the opponent specifically had graveyard-hate prepared. I think the last ability should have at the bare minimum a "activate only once per turn" clause, if not also a "and only during your turn" or even "only as a sorcery" clause as well.

{Spoiler}Good on ya for bringing a less seen type here. At first I thought this card was pretty weak considering a mana cost of 6, but then I realized the cost is probably with commander or other multiplayer formats in mind where you could be drawing like three cards each turn. I like how the commonality of thopter exploration and sphinx knowledge was used to keep a stable flavor with a very simple ability. I do wonder what the flavor of needing more thopters is though.

{Spoiler}Before anything else, I need to say, that's an awesome choice for an image. I don't usually comment on that because renders are not mandatory and the art here isn't really something we made (most of the time), but when something's this nice ya gotta throw it a mention.

That aside, I'm not really sure on the wording of that second ability (at the very least I know there is no official wording like that), but it is absolutely awesome as well. It's a very unique effect that oozes flavor from the combination, and synergizes in a really elegant way with the second ability, that is a classic of blue. In general the card fits very well both colors and types and has some fun unique abilities. Love it.

{Spoiler}I'm giving this victory to melono for a card that just appealed to on a number of levels, from aesthetic to unique mechanics, great flavor and so on. The runner-up spot is for pernicious who had a pretty good card that I think was just slightly off being balanced and good to go.