how can i check if my iphone 7 plus is new or refurbished?

Open the “Settings” app on the iPhone

1. Go to “General” and then go to “About”
2. Look for “Model” and then read the model identifier next to that text, it will look something like “MN572LL/A”,
3. the first character will let you know if the device is new, refurbished, replacement, or personalized:-

• M – Brand new device, meaning the device was purchased new
• F – Refurbished device, meaning the device has been through refurbishing process
• N – Replacement device, meaning the originally bought device was replaced by this model likely due to a service request
• P – Personalized device with engraving, meaning the device was customized with an engraving on purchase

iPhone Model Number

If the model number of the iPhone starts with the letter ‘M,’ then it is a NEW iPhone. If on the other hand, the model number starts with letter ‘F,’ it’s a carrier-refurbished model and when it starts with the letter ‘N,’ it indicates that it is an Apple Replacement device.

This is different than the model number that you find printed on the back of the iPhone starting with the letter ‘A.’

Finding the model number of your iPhone is easy. Tap on Settings > General > About and scroll down to the Model section. This setting will show you the nine-digit model number that you can use to determine the origin of your iPhone.

• M – your iPhone is new 
• F– your iPhone is refurbished (refurbished by Apple or a carrier)
• N – your iPhone is an Apple replacement phone
• P – your iPhone was personalized with engraving

On newer iPhones such as the iPhone 8 and higher, the model number is also visible in the SIM tray slot. You will need to remove the SIM tray and look.

Buy your phone directly from Apple.

If you bought it directly from Apple or an AUTHORIZED retailer, then it's new. If you bought it from an individual or an unauthorized retailer, all bets are off... the only thing that can definitely be said in that case is that it is not "new".

Even if you buy directly from Apple, there is a clearly marked section for Refurbished devices.

But if you go to the "sponsored" page or the main device page, it is guaranteed to be brand-spankin-new!

Just curious, are you posting on an iPhone or iPad and were you able to see the response from AzizBhimaniMax above?

On a PC and by the time I got the answer I was late as usual:)