How do I link my iPhone to my MacBook?

Depending on 'why-or-how' you intend on linking these products together.

And the intent is an important factor in attempting to answer this question.

By wire, for certain purposes; wirelessly for other uses. Trying to backup by USB?

Trying to restore from backup by wire? Hard to answer without specific question.

Are you trying to use features such as air-drop, image sharing, etc between iPhone & Mac?

• Use Continuity to connect your Mac, iPhone, iPad, iPod touch, and Apple Watch - Apple Support

https://support.apple.com/en-us/HT204681

Harder to sleuth an answer ~ when there is no clear question.