Why do some cats answer the phone? They don’t. There is some other explanation unless someone has a clever idea.
Below are two examples of cats answering phones. In the second video, the cat brings the mobile phone (cell phone) to the person. There is probably some human intervention in this video when the cat goes out of sight. In fact, my impression is that the whole event is set up and the cat trained to certain extent to jump down when the phone rings.
The TV presenter in the first video suggests that the cat knocks the phone off the hook to stop it ringing. This is not an example of a domestic cat answering the phone, obviously, but a cat silencing a noisy object. The cat has learned how to do this. This is my best guess.