If you receive a FaceTime video call on your iPhone, the handsfree will be activated immediately after you answer if you are not wearing a headset. It's exactly the opposite when it comes to FaceTime audio calls, but it's pretty easy to fix it if you'd rather use the handsfree instead of the built-in earpiece.
Before we start, some things that you should keep in mind. If you are connected to a wired headset or a Bluetooth device, all audio data is transferred from these devices regardless of the option set. Second, the following instructions also make the speakerphone the default setting for normal phone calls. You can not change this setting for Phone or FaceTime individually.
If iOS 1
2 or lower is running, go to the "General" section of your iPhone's "Settings" app, and then tap "Accessibility." "On iOS 13, go to" Accessibility "in the Settings app.