I'd like to share passwords between macOS and iOS. I've enabled iCloud keychain, moved all relevant passwords in Keychain App to iCloud but for some reason they don't appear in my iPhone. I check my passwords and there's nothing there. How can I debug this?
Keychain must be turned on in both iOS and macOS. While data is moved back-and-forth through iCloud, data is not accessible from iCloud and need not (and should not) be moved manually from a computer or device into the user's iCloud storage. You can see Apple's directions for iOS here, and for macOS here. A good long-form discussion of Keychain synching is here. Apple's iOS page notes that Keychain synching is not available in all countries.
Turn on Keychain synching on your iPhone in Settings > iCloud > Keychain. The Keychain slider must be "On." (This is iOS 12.2; your iOS may vary.)
Turn on Keychain synching on your Mac in System Preferences > iCloud > Keychain. The checkbox next to "Keychain" must be checked.
Confirm that both the iPhone and the Mac are signed in to iCloud.
You don't need to manually move files; it all happens seamlessly behind the scenes.
Only passwords stored via Safari are synced between devices. Passwords manually added to Keychain App are not sent to iOS.