I see you are asking about priorities. That is not my issue and you don’t mention auto connecting to a tethered phone. Since this is the only internet source, priorities is not the issue. The real issue is when tethering is engaged on the phone, the router auto connects to that source rather than requiring the use to go to the internet connection page on the router and clicking the ‘Connect’ button.
The clicking of the ‘Connect’ button is what I am asking about automating, not priority.