Default [Q] google 2 step verification

I have my enabled 2 step verification process enabled for my google account. In this i use the G authenticator app on my mobile to generate numbers to authenticate for 2 step process. This works fine if it is prompting for number in my desktop pc browser where I can use the mobile phone app and key in the numbers. But sometimes i am asked to sign in to my account in mobile phone for which it prompts to enter number from g authenticator. Now i cant open the g auth app without cancelling the current prompt. So in effect i am never able to authtenticate to mobile google account 2 step porcess.How to authenticate myself with g auth app when prompted to enter number in mobile phone ?