I guess it all depends on what you mean by a phone. For me a phone is something which allows me to make/receive a phone call (at the very least) - to any phone

I guess it all depends on what you mean by a phone. For me a phone is something which allows me to make/receive a phone call (at the very least) - to any phone number without requiring some special software to be installed on either end of the phone call. For instance, even on a cellphone, I distinguish between calls made directly via the phone dialer vs Whatsapp video/audio calls or any VOIP call - because the other side has to have a compatible/supporting application/app to receive that call.