You don't need to accept any phone call from a user as you will need to enable first their capacity to call you before they can do so. In order to enable phone (or video calls) from another users, simply go to the chat conversation with this user and click on the $ at the top right of the conversation. You will be able to select what contact methods you want to offer to that user.
Note: if a user joins the platform and had already your phone number in their phone contacts, they will by default be able to reach you over the phone (as they could call you regularly). You can still change that by simply opening a conversation with that user and clicking on the $.