I just want to know my date of purchase of my Apple 7 plus phone

Look at the receipt.

There is no way to determine the purchase date without it unless you purchased it new and it's still under warranty or AppleCare+.

Enter the serial number here: https://checkcoverage.apple.com

Mimiofloonlake Said:

"I just want to know my date of purchase of my Apple 7 plus phone: I want to find out the date I purchased my Apple 7 plus phone. I have the Serial Number. “

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Contact Apple Support:

I don’t know if Apple Support would have access to this, but give them a call. Provide the Serial Number to them. If permitted, perhaps they could tell you.

• Contact Us - Choose Locations
• (U.S.A): (800)MY-Apple
• Ask to speak with the Apple Store Staff
• Proceed from there as necessary

Why the Wait:

Phone calls are taking a bit to go through at the moment, due do lots of calls. With the Coronavirus Pandemic, many are at home at the moment, with much time on their hands to contact Apple. So, just stay on the line, and you will get through :)