tl;dr Yubikey 5 NFC works great with 1Password on iOS (assuming your phone has NFC).
I just got 1Password to use on my iPhone and my Mac. The website allows using a Yubikey as a second factor (in addition to apps, like Authy or Google Authenticator). Turns out, the iOS 1Password app also handles the Yubikey 5 NFC properly: open the app and it asks for the password, and then for the second factor. If you scan your Yubikey using NFC, the app recognizes it.
The alert pointing to the special website also appears, but it is not necessary to go to it.