I don't think the Sputnik V vaccine has any substantive relationship to phage research and therapy. And I don't think there's much reason to doubt that Russian researchers could develop a solid vaccine, if only because it's difficult to say with strong confidence which approaches would definitely fail. Rather, it's a question of whether they actually did given the political dynamics. There's good reason to discount the credibility of claims coming from authoritarian regimes. (Reasons for which most Americans have a renewed appreciation, rightly or wrongly.)

I suspect it wouldn't be too difficult to fudge the numbers (e.g. candidate selection criteria) in such a way that a mediocre vaccine looks excellent. Until it's reproduced or until other opportunities for falsification arise, trusting a result is largely a matter of the personal credibility of the researchers and, importantly, the system in which they operate.