When they say "get an iphone 16 on us" what exactly does that mean...

I recently transferred my phone to Xfinity mobile and was never told about this iphone 16 on us deal.  I have an iphone XR and would love to upgrade but I need to know exactly what "on us" means.  Free? Discount if I trade in my current phone?  Which won't be much because my phone is an xr which is old.  So what deal can I get?  So far i'm very happy with Xfinity mobile and would love to stay but if I can get an upgraded phone with someone else I just might do that.  Looking at all options possible.