I'd like to switch my Apple TV account from my iphone to my home TV. How do I do that

Your Apple TV+ subscription is associated with your Apple ID, and is available to all of your authorized Macs and your authorized devices from there, and is also available to members of your family through Family Sharing.

If your Apple TV app or Apple TV hardware is logged into the same Apple ID, your Apple TV+ subscription already available to other devices logged into your Apple ID.

If you have purchases and subscriptions across more than one Apple ID, there's no way to consolidate those. One potential work-around for that—pending migrating the Apple TV+ subscription to a different Apple ID, which would be typical here—is to configure and use Family Sharing.