AirPods Pro 2 controls stopped working with iPhone

My AirPods Pro 2 controls have suddenly stopped working with iPhone. Still OK when connected to MacBook Pro, but pause/volume control just has no effect when playing content from phone (eg. Spotify, Audible).

I can hear that the control is being recognised with a click sound, but nothing actually happens.

I've tried forgetting and then reconnecting, also resetting the AirPods.

Anyone else had this?

iOS 18.7.3