Yes!!! The chessbase app is a Must. You only pay once. You get the newest games in the database within a couple of days. Searching is not trivial. I can help. I only know Android. I assume iOS is the same.
iOS phone database

Michael. Thanks. That might be the ticket. For some reason, I just assumed I needed to be subscribed to their online platform to use it. Does it require internet access from the iPhone? The chess clubs I frequent are sometimes dungeon-like, and I can’t get internet.

Unfortunately, I don’t think Lichess’ database is downloadable straight to the iPhone. Would be a great option, otherwise.
im at the point where I’m getting to know my repertoire options well, and I am occasionally able to know my opponent’s openings before an OTB game. I’d love to be able to look at some continuations that have been tried. Is there an extensive games database that is a one-time purchase (not requiring subscription renewal) that is particularly popular?