I think that Euclase will be presented as a sensible but stolid loyalist in contrast to reckless but revolutionary Phos.
From what little we've seen so far, Euclase is essentially a bureaucrat, maintaining what exists. Which is not necessarily wrong, and seems very sensible and certainly less destructive than Phos's mad probing and poking at all the secrets of the world.
But I think the point of this contrast for the plot is that it's the brave and great and perhaps terrible catalysts like Phos that break open the path to enlightenment.
We might see more of Euclase in the future where he becomes more of this mastermind strategist, but that hasn't happened yet and might never happen. Right now he's just a bland gem doing his job.