'Jungling' isn't the same in 3v3 like it is for 5v5. It's not a phase.
Lantern is awesome for Lee in 3v3 because it lets you clean up monsters in the brush in a matter of moments, while moving from lane to lane to push and help your allies in ganks and teamfights.
If you want to be really effective in 3v3's, you should always be killing jungle mobs whenever you get the chance. They provide a huge gold and XP boost, as well as very powerful buffs. A Lee Sin with 180 creep kills at 20 minutes is much more effective than a Lee Sin with 90 creep kills at the same time.
Think about it. The Lantern makes killing those mobs both quick and painless. And, it gives you a free ward.
If you avoid the jungle altogether in 3v3's, you will do much worse than a Lee who uses the entire map.