With iOS devices, when you make a phone call using your iPhone, you also have the option to turn on FaceTime assuming that the other user has FaceTime enabled. This is something that Google is trying to do with Duo as we have seen from an previous APK teardown, where Google is looking to integrate Duo with Android’s Phone app.
Now according to a report from Android Police, it seems that Google has finally integrated Duo into the Phone app. It does not seem like there needs to be any action taken on the user’s end because according to the report, the video call button just shows up. Switching to a Duo call is pretty straightforward and all users have to do is tap the button and it will launch the Duo app instantly.