How to get my phone to access WIFI channel 13?
My phone can now detect ch 13 on 2.4 GHz wifi. 

Here's how I did it. I borrowed a local sim card. As soon as the phone booted up, if was able to see the wifi signal. I confirmed that it indeed was on ch 13 with both wifi analyzer and on my pc.

I have since removed the borrowed sim card, and the phone continues to see channel 13. So indeed, as suggested in the comments by @Robert, 


  auto detection of the country you are in e.g. via used SIM card


Is the correct answer.