Can the phone automatically switch to the mobile network when Wi‍-Fi is absent or weak?

Yes. You can set the phone to automatically switch to a mobile network when there's no available Wi‍-Fi network or the signal is weak.

1. With two fingers, swipe down from the status bar to open Quick Settings.
2. If the Wi‍-Fi connection is off, tap the Wi‍-Fi tile to turn it on.
3. Tap .
4. Tap > Advanced.
5. Select Auto-switch to mobile network.

Note: This feature may not be available in some phones.