No. How would someone be "linked" to your phone? It's not possible unless they knew your Apple ID and Password to access iCloud settings. If they really were linked, the other device would show up under other devices that are all using the same Apple ID and Password.
So, it would take no more than a few seconds for you to check and see if an "unknown" device was using your Apple ID and Password. On your iPhone.....Settings > (Your Name) > Devices
If you are really concerned, you should set up your router to provide "fixed" or "static" IP addresses for each of the devices on your network. That way, you always know what exact IP address has been assigned to each of your devices.
An "unknown" device would not even be able to connect to your network unless you allowed it.