How about we define "phone" as a voice capable device that is reachable by its assigned phone number. It's the unifying factor for dozens of different technologies that have been called "phone" for decades.
Unfortunately you can't actually just pick a definition for a word based on what makes sense to you. Definitions are decided collectively by all speakers of the language, and the definition I gave is actually a fairly conservative one.
Plenty of people actually use "phone" to mean not only "cell phone" but specifically a "smart phone" and feel the need to qualify it if they mean a "dumb phone". Like it or not, that's the way the word is going.
Some people do. Others don't. Why would you get to decide which usage is blessed?
Like plenty of people talk about phone calls that only take place on zoom or meets without ever using a smartphone or dumb phone (but the call is joinable via an assigned phone number)
In most settings that question includes an implicit "cell"! They're not asking if they can go home with you and use your landline, they're assuming you have a phone in your pocket with service.
A landline is a type of phone in the same way that a panda is a type of bear. Technically it's true, but if you say you went to see the bears at the zoo it's your own fault that people aren't picturing something with black and white splotches.
Anything else seems absurd.