Turn off Find My Phone without icloud or phone

I have a customer who is needing to file an insurance claim on an iPhone he got for a girl. The find my phone is still on but the phone is completely shattered and won't turn on. She will not give him the icloud info that is logged on in the phone. He has another iPhone device I can active on the MDN. Is there a way for him to locate what icloud account is logged in just with a working device and phone number?