I know 3 phase is 120v line-neutral, and 208v line-line, but what is it when
all three lines are used? Or is it just not referred to at all, since
voltage between three lines doesn't mean anything?

Can 208v be called 2 phase? I know 2 phase is properly an obsolete system
that involved 2 120v line, 180 degrees out of phase; but is the term now
ever used for 208v?