Yes some phones only support frequencies, but modern phones pretty much support everything. You need to validate the carrier and phone you choose are compatible, but odds are they will be. It’s not a region lock, it’s just a limit on the radio frequencies they support.
This is carrier locking, not region locking. A phone bought on a discount from carrier X will be locked so you can’t stop paying them and just move to carrier Y.
This is done at the play store / apple store level for specifics apps that are banned or not available in a location. The code for this is not on your device, and you can sideload to get around it.
Tldr: make sure the phone supports the frequency of the carrier that you plan to use, and that its not been carrier locked. If it is, you can probably buy an unlock code online. Then you’re golden.
5 seconds on Google answered your question though op. New phones from Samsung are region locked until you make a 5 minute phone call in the source country. That way people can’t buy phones in cheap countries and mail them out. This seems fairly new, I’d never heard of it until now and I’ve imported phones in the past.