SOLUTION FOUND for my case.
I realise this is a Necro but found a solution to my problem. My great work stalled in phase 1 when I "closed" / "removed" the advisor buttons from the right in the city screen that was sending resources to the great work. When then viewing the great work it showed as stalled & showed the 3 resources as "off". I tried switching them on but it still showed as stalled. What I had to do was keep them off, log out the game. Then when I logged back in it no longer showed as stalled & I could switch them back on & it continued as needed. Hope that helps someone. Maybe there is something similar for phase 2 that can be done?