I don't know which phone you're using, but on my pixel if I have my ringer volume on silent, and the phone on "do not disturb" mode, amber alerts come in silent

I don't know which phone you're using, but on my pixel if I have my ringer volume on silent, and the phone on "do not disturb" mode, amber alerts come in silent. I'm not sure which one, or the combination actually silences it since this is usually how I keep my phone when the alerts happen to occur.