PHONE EXPERTS OR BESTBUY WORKERS

Ok so 2 years ago I got a new iphone 6s at Bestbuy and there was a deal where I can get it replaced after 2 years for free but like I have alot of stuff on my phone so how does it work like if I get it replaced do I lose everything on my phone?

You use your apple account to back everything up, and then when you have your new device you restore to that one!