How do I direct my backup to an external drive on my MacBook Sir running Ventura 13.0.1

AFAIK the iPhone Backup can not be directly to backup to an External Drive Directly from within Finder

The may be able to track down where the backup is located on the Internal Drive via the below Instructions from Apple.

There after >> Copy the Backup to the External Drive

Locate backups of your iPhone, iPad, and iPod touch - Apple Support

Excerpt from above link

Copy backups to another location

If you need copies of your backups, you can find the Backup folder and copy the entire folder to another place, like an external drive or network-storage location.

Time Machine automatically copies your Backup folder when you back up the Home folder on your Mac.