What are you trying to protect against in this case?

If your phone gets stolen and it's logged in to your google mail without a lockscreen pin/code, then yeah - the thief can read your mail, 2fa won't help. They can also run your Authenticator app and see the current 6 digit number, but that's not useful without the password as well.

(I'm not sure how easy it is to extract the Google password from an Android or i phone - I wonder if you can just switch them to non-TLS POP3 or IMAP and have them send a cleartext password over an unencrypted wifi connection?)