Machado will be a free agent in October if he's not traded (and quite possibly even if he is!). If the Orioles don't trade him, they'll get a compensatory draft pick, and nothing else.
Given that they know this, their interest is to get the best deal they can for Machado - assuming only that they get something more valuable than a draft pick in the 31-34 range. Their only task is to get the best deal they can, which is likely to only be available until the trade deadline (Machado isn't going to clear trade waivers after August 1 - I assume the Phils would submit a claim, and I doubt they'd be the only club to do so). So I strongly doubt Machado will be in Baltimore on August 1st.
I don't think it's a question of what the Orioles "expect" in return. It's a question of what the various interested clubs will offer, in what is essentially an auction. It's in the Orioles' interest at this point to posture a bit about what they "need" back - but what they'll accept will meet two critera (and two only, IMHO): 1) it's more attractive than a 2019 compensatory draft pick; and 2) it's the best offer they have as of the trade deadline.
Given that they're playing an auction game here, the existence of the deadline, and auction psychology, suggest that Machado will not likely be traded much before the deadline. The Orioles' interest here is to hold out for a "better deal," allowing the bidders to get a bit anxious, and maybe a bit irrational, as the deadline approaches. If a club (Phils or other) wants Machado sooner, I would think they'd need to pretty much "blow the Orioles away" with an offer that's beyond what they realistically think they can leverage at the deadline. Do we want the Phils to attempt that?
Downside risk for the Orioles? I guess the chance that a bidder will just give up, and make a deal for a Moustakis (much inferior, but maybe "good enough" for a bidder) instead. Of course, also the chance that a bidder will go on a 15-game losing streak, suddenly realize they're no longer in contention this season, and drop out of the bidding. But if there are several interested bidders, these are fairly minimal risks for the Birds.