Based on screenshots in the announcement of 5.0 iOS app, we should be able to select premium fonts in the app using the gear icon at the top. But this does not appear for me. Gear icon at the bottom on feed list shows Preferences (only font size is an option there), Find Friends, and Logout. Gear icon on a folder shows Delete, Move, Rename, and view options for order and unread. Gear icon on a feed shows Delete, Move, Rename, Train, Insta-fetch, and view options.
Maybe this got left out of the views for smaller screens? Does it need force-push devices?
iPhone 5S; iOS 9.1; I was on the beta build, but stopped testing (it was listed as 4.9.something) and grabbed 5.0.0 from the app store.