How do I know what career my phone is locked to

Ask Amazon.

If they cannot provide this basic information about the phone, return the phone for a refund.

You would never want to buy a "locked" phone from any seller unless you know who the carrier is and you want to continue service with that carrier.

Your best bet would be to make sure that you buy an "unlocked" phone, so you can choose which carrier that you want to use.

For new phones sold by Amazon, they will always specify whether it is unlocked or the carrier it is locked to. With other third party sellers on Amazon, you will need to contact them. Your best option may be to return the device if they are unable to provide that information.

Ask the person/agency that sold the device to you.