Hi lunameyo,
Thanks for using Apple Support Communities. The Siri voice on your AirPods should match that which is set for the paired device. So, in this case, since you're using your iPhone with your AirPods, you can use the following steps from Change Siri voice or language - Apple Support to change it.
"On your iPhone, iPad, or iPod touch
Go to Settings > Siri & Search.
Tap Language to change the language that Siri uses for requests and responses.
Tap Siri Voice to change the voice that Siri speaks.
To hear spoken responses from Siri on your device, tap Settings > Siri & Search > Siri Responses."
All the best.