Full phrase, "... treating Genesis 1 as a non-material account of origins to allow for these supposed millions of years."

There are variations you could use, too, depending on your chosen register, though "treating ... as" is one of the simpler ones. You could also do "interpreting ... as", since there's fundamentally complex text interpretation going on when perusing Genesis.

In literary theory, there's an interesting concept called chronotopes that attempts to study how time is portrayed in literature, including the Bible. The original progenitor was a one Mikhail Bhaktin, whose work you may find useful when working with time and literature (see reference link for more details).