Use the power of each of those creatures at that time, even if the creature is no longer attacking or no longer a Phyrexian
Believe it or not, there are people out there who love Commander, who DO NOT like building decks
I can imagine winning with a big Stella, sure, but I can also easily imagine that not working, which is why the deck doesnt support that plan, really, and why other cards which also do that plan, Malevolent Whispers and Mark of Mutiny are left out
Eerie Interlude, Flickerwisp, and Ephemerate are all excellent ways to eke out value in the early game (flickering smaller creatures like Wall of Omens), and then dash your opponents hopes later in the game by abusing more powerful effects
Cest la vie
But to help satisfy your curiosity, Ive studied each era of the game and arrived at what youll see below the absolute best cards that will (or wouldve) let you win plenty of tournaments, or just crush your friends during casual game nights