Check the temperature on your iPhone

Are you referring to their operating range, as in what temperature range the device will operate in? That information is available from the iPhone specifications section, accessible from the iPhone page. If you are talking about the temperature the device operates at when in use, that information is not available anywhere that I have ever seen.

Check this link, https://www.apple.com/iphone-7/specs/ under Environmental Requirements.

https://www.apple.com/iphone-7/specs/

This app tells the battery temperature: https://itunes.apple.com/ca/app/battery-percentage-check-devices-runtimes/id1199 284304?mt=8

I don't believe you are going to find that. I've never seen it before in any of the specification sheets for the iPhone. You can contact Apple Support and see if they can share any information with you, otherwise you may not get it.

What do you mean "official"?

iOS does not provide this info to the user.

Some apps might be able to use API's to access this data