How can I end calls using voice control on iPhone

End calls with Siri

1. Go to Settings > Accessibility > Siri, tap Call Hangup, then turn on Call Hangup. Note: Available in select languages and on iPhone 11, iPhone SE (2nd generation), and later. ... 
2. To end a call, say something like: “Siri, hang up.” (Participants on the call will hear you.)

Change Siri accessibility settings on iPhone - Apple Support

In addition to the above recommendation from SravanKrA, if you are able to, then you can Double Tap the Screen with Two Fingers to end the call.

Axel F.