HomePod volume control interferes with iPhone audio

I play an album on a HomePod in my kid’s room for him to sleep to, but I can’t listen to anything on my phone or even adjust the volume of my phone independently- it always defaults to the HomePod. It’s SO frustrating. It is literally the dumbest thing my smartphone does. Occasionally the “control other speakers” button randomly allows me to ‘disconnect’ from the HomePod (without stopping the music on it) so I can listen to a video or even turn my phone up or down without turning the HomePod up or down, but it doesn’t consistently work.

[Re-Titled by Moderator]