Can we agree on setting up some standards […]?
I wonder why? What problem are we trying to solve? I mean, it's not like I can edit the priority of a Phabricator ticket and expect some other team to act accordingly. This is not how cross-team collaboration works, neither with nor without an agreed on standard.
It's not helpful anyway. Who decides what priority a ticket should have? Based on what information? Which ticket should I pick first when I have hundreds that claim to be high?
Our team stopped using the priority field entirely. Well, with the obvious exceptions, namely "unbreak now" and occasionally a low(est) priority to communicate that there are currently no plans to ever assign resources to a ticket. Instead we use boards to model products, teams, and sprints within a team and order tickets in columns from top (high priority) to bottom (low priority).
I believe what we are really discussing here is what https://www.mediawiki.org/wiki/Developers/Maintainers stands for and partly solves. A ticket alone doesn't do anything, no matter how we prioritize it. Ownership and responsibilities are what matters.
I support dropping "lowest".
Best Thiemo