"Hey Siri" responds only on shouting too loud.
My newly purchased iPhone 14 doesn’t respond to "hey siri" despite following all procedures and troubleshooting.
Retrain Siri with your voice
Go to Settings > Siri & Search, turn off Listen for “Hey Siri,” then turn on Listen for “Hey Siri” again. To change Siri accessibility settings, see Use accessibility features with Siri on iPhone.