Apple Watch - steps are not accurrate unless i have my cell phone - why is that?

Hi

To help improve the accuracy of estimations for steps, calories and other results:

Check that your iPhone and watch are updated with the latest software:

• Update the iOS software on your iPhone, iPad, or iPod touch - Apple Support
• Update the software on your Apple Watch - Apple Support

Check that you have set up the Activity app on your watch:

• When viewing the time on your watch face, tap on the Activity rings icon / complication, or;
• Go the Home screen (via a single press of the Digital Crown) and tap on the Activity app icon (coloured rings).
• To get started, you will need to enter some personal information.

Check that you have enabled Wrist Detection:

• On your iPhone, in the Watch app, go to: My Watch > General > Wrist Detection.

If you have also enabled Passcode, ensure that you unlock your watch after placing it on your wrist.

Check that your personal information is accurate:

• On your iPhone, in the Watch app, go to: My Watch > Health > check and, if necessary, edit your birthdate, gender, height and weight.

Check that you have enabled Fitness Tracking:

• On your iPhone, go to: Settings > Privacy > Motion & Fitness - check that both Fitness Tracking and Health are enabled.
• On your iPhone, in the Watch app: My Watch > Privacy > Motion & Fitness - check that Heart Rate and Fitness Tracking are both enabled.

Calibrate your watch, which will improve the accuracy of health and activity-related estimations:

• Calibrating your Apple Watch for improved Workout and Activity accuracy - Apple Support

More information:

Use the Activity app on your Apple Watch - Apple Support

Use the Workout app on your Apple Watch - Apple Support