Adding devices to my Apple ID
I have got my iPhone, my iPad and my laptop on my Apple ID but I can’t figure out how to add my wife’s phone to it.
iPhone 7, iOS 15
Question marked as
You would have to sign in with your ID on it to add it to your account. That's a bad idea since she should be signed into it with her own account.
What's your underlying reason for wanting to do this. Probably Apple has some otehr means for achieving what you want, such as Find My. Learn how to use the Find My app to share your location with friends and family members. You can even set up location-based notifications, so that you know if someone left a location or just arrived home. Refer to the document:
Find friends and share your location with Find My - Find friends and share your location with Find My - Apple Support