Turn of find my iPhone on broken phone

See “Erase your device” here.

If your iPhone, iPad, or iPod touch is lost or stolen - Apple Support

You can turn Find My OFF from going to your iCloud account with use of another computer or another Apple Device.

Just open ➔ www.icloud.com, log into Your account and go to "Find my iPhone". On the top You'll find a list of all devices in Your iCloud, just click on the one You want to remove and chose remove from account. Once removed then Find My will be OFF on that device.

Axel F.