Apple has had a feature called Apple Data Detectors since the 90's that looks for different patterns in text and allows you to perform actions on them.

So if the text includes a phone number, email address, flight number, package tracking number, street address or other pattern in the data it is underlined and allows you to perform one or more actions.

The patterns it looks for and actions it takes are extensible by developers.

If you don't care for it, you can turn it off.