Music & Call simultaneously

If you are use AirPlay from the phone then no, that will be suspended during the call. If the HomePod is streaming content independently of the phone, e.g. from your purchase history or iCloud Music Library if you have Apple Music or iTunes Match, then making or taking a call won't affect the music.

tt2

Does this also apply to HomePod Mini? I want to get one for my room just to chill with Apple music and also be able to FaceTime at the same time.

That should be fine.

tt2