You no longer need to install a third-party keyboard to be able to swipe to type on the iPhone. After years of seeing this feature on Android devices and recently on third-party keyboards it is now integrated directly into the iPhone keyboard.
With this new keyboard, you can slide your finger across to letters to type. So far it feels accurate and it does a pretty good job, but on the beta it isn't handling contact names very well.
If you don't like this feature you can just type normally. Users that accidentally trigger it can turn it off in the iPhone settings.
On iOS 12 you can install many third party keyboards that allow you to do this, but you have to toggle to them and you don't get the system level integration that Apple now offers in iOS 13. You can still continue to use third party keyboards if you prefer what they offer.