Trade-in
How can I send my phone for a trade-in if I am from another country?
Question marked as
Take a look at this page which shows the Trade in (Apple Give Back) vs Recycle-only (no trade in value, just disposal) options available through Apple in every country:
https://www.apple.com/uk/recycling/nationalservices/
Only countries with an Apple Store (or possibly direct Apple.com sales) may have a Trade-in value since you only get Apple Store credit.
However, if you are specifically looking for the most value you would be best off selling your device to a private buyer.