I WOULD LIKE TO KNOW WHEN MY PHONE WAS PURCHASED

This is a user to user forum and Apple is not here. We do not have that information. Look on the receipt you got when you purchased your phone.

A quick online search turned-up several ways to determine your phone’s approximate production date.

(The accuracy of any of these methods is unknown)

While not exactly the “purchase date” … it might still be of some help to you.