Steps are being counted on both devices (Apple Watch and iPhone)

I recently bought an Apple watch and paired it to my iPhone X. The health app has been adding steps twice for the same period. I do a 30-min brisk walk everyday in the evening and at this time I am wearing the Apple watch and the carrying the iPhone. In a 30 min period, the health app added up about 6000 steps (which should have been only 3000).

Could anyone suggest me whats wrong with the Health app and what is a corrective measure to sort the step counts?

Thanks!