Given the festival boom of the 2000s I'm surprised nobody tried to revive the Phoenix Festival branding. Well a now-closed pub near to me called the Phoenix had Phoenixbury Festival for local dad bands but it's not quite the same.
I thought T in the Park went because of circumstances, given they got kicked out of what was a useful site for reasons out of their control and the new site picked was crap, so the promoter just created TRNSMT instead. Maybe actual Scots have a better guide to that.