Adjust AirPods’ volume during a call using Crown of the Apple Watch

when I am in a call using my AirPods Pro, (at the same time, with my Apple Watch on my wrist and my iPhone inside my pant pocket), I could NOT adjust the call volume using the crown of my Apple Watch. Instead, I can do so only through my iPhone.

indeed, from a user’s view, it’s be easier and more friendly if I can change the call volume using the Crown. So that for example I don’t have to take out my iPhone from my pant pocket to just tune the call volume.

note: my Apple Watch is series 6, and it’s “GPS” edition (NOT “GPS + cellular”).