6s screen doesn't turn off during calls via speakerphone?

[DKO110]

If I'm on a call via speakerphone, the screen dims but doesn't turn off even if I hit the power button. I'm assuming this is as intended but just want to make sure.

 

[321estrellas]

Things could have changed but years ago when I used the speakerphone a lot, I thought hitting the power button locks the phone and turns off the screen?