Changing default phone for Google login device
Go to myaccount.google.com, sign in and click on Sign in and Security.

Scroll down and go to Account Recovery Options and click on Recovery Phone

Add/remove the phone numbers according to your preferences.

Then go back, scroll down and click on Recently Used devices and remove all the devices that are not in use. If your Iphone is not displayed here then make sure that you've signed in in your IPhone with Google Account.