Can I still activate my phone if it’s already set up

I don’t quite understand your question. If the iPhone is currently set up to someone else’s phone number and Apple ID, you will have to ask them to deactivate the phone. Until that is done, you will not be able to use the iPhone.

Okay, now you are making no sense whatsoever. Where did you get this phone? Did it belong to someone else? Have you called US Cellular to find out? If not why not? You’re starting to sound suspicious.

If you obtained this phone from another individual they will have to properly erase and deactivate it before you can use it. If it’s in Activation Lock you will never be able to use it without the original owner’s cooperation.

Well, you should be able to but not through Apple. Apple does not offer a cellular plan and is not a carrier. You have to contact a cellular carrier in your region to discuss plans and prices.