Do I need to keep my phone's Bluetooth enabled all the time when wearing my watch?

1) You do not need to enable Bluetooth all the time for features such as step counting, workout, sleep monitoring, heart rate measurement, blood oxygen saturation measurement, timer, alarm clock, idle alert, and PAI calculation.
2) You need to enable Bluetooth for features such as calls, app notification alerts on your phone, phone finder, watch finder, and music control for your phone, since the phone needs to promptly transmit information to the watch. These features can be used only when your watch is connected to your phone.