Are you able to use HomePod with your iPhone (Answer Calls)?

Answer a call: When your iOS or iPadOS device rings, say “Hey Siri, answer the phone.” Before answering, you can ask “Hey Siri, who's calling?” End a call: Tap the top of HomePod, hang up using your iOS or iPadOS device, or say “Hey Siri, hang up.” (Other Siri requests aren't supported during phone calls.)

Use HomePod for phone calls - Apple Support