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

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, timing, alarm clock, standing reminder, and PAI calculation.
2) You need to enable Bluetooth for functions such as calls, app notifications 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 functions can be used only after your watch is connected to your phone.