how can i tell if my iphone is linked to another device
how can i tell if my iphone is linked to another device
iPhone 6s, iOS 10.2.1
It is not. You can't "link it" to any "device" other than your computer running iTunes. Well, and things like bluetooth headsets.
What you want to find out is what devices are signed into your iCloud account / Apple ID.
Log into your account at https://appleid.apple.com
You will see on that page what devices are signed into your account.