How do I remove a device from my phone? I just got the new 14 but it’s still showing me is having the 12.

Transferring often gives your new phone the same name as your old phone … usually w/ a parenthetical number appended … often causing confusion.

So, first rename your new device to something clear and unambiguous to YOU: Settings -> General -> About -> Name. (e.g. jfbiph14)

Then … login to https://appleid.apple.com/ choose devices … and delete any old/non-active devices which might still be there.

Lastly, don’t forget to “wipe” your old phone; either w/ the erase section of “Quick Transfer” or by this procedure:

What to do before you sell, give away, or trade in your iPhone or iPad - Apple Support

You’ll probably need to power-off and restart your device to get it to accurately “sync and display” on https://appleid.apple.com/

Make sure to use a new browser window too.