I want to update my phone to iOS 16

If this is about the iPhone 7 in your equipment profile, it is too old to support any iOS version higher than 15. See:

If this is not an iPhone 7 as shown , please post its model.

If you have an iPhone 7 Plus, as indicated, it can be updated to iOS 15.8, no further.

You will need an iPhone 8 or higher model if you want to update to iOS 16.

No go with an iPhone 7 Plus.