Indeed you can. When you do you simply get teleported to the Nexus. :)

I'm surprised no-one has commented on this since the game is now released, assuming people have bought it. I got it yesterday myself and have beaten Phalanx, plus the first boss of Stonefang Tunnels. (I've been into each world so far, but Stonefang is the only one I've tried beyond the first couple of enemies)
I'm really enjoying the game, but I do keep dying a lot. First death came against a certain knight in the first area. I chose a Knight to start out with, so I'm not exactly able to roll about quickly until I can raise my equip burden cap, unless I wear lighter armor. I find moving back after locking onto enemies as they strike (or just before) works well though, as does blocking with my shield. The 'riposte' move is also an option provided I get the timing right, which is something I don't go for too often unless it's against one of those knights in the first area. I'm loving my heal spell now as well which I just gained, mainly because I can farm easy enemies now and quit expending as many healing items so I can build a stockpile of them.
As a side-note, I've killed a few Black Phantom NPCs so I'm able to invade others now if I wish (probably won't as I'm not a pvp person). But I've yet to actually be invaded by another player yet. Currently soul level 17 I think. It might have something to do with the fact I've had my body for all of two seconds though, the two times I've retrieved it. ;)
And people in the EU have already cleared the game apparently... I'm guessing they either imported it earlier and bought it again or just rushed through the game. Not sure how they could get through it so quickly without having a guide open all of the time though (which is something I'm trying to avoid after spoiling the first area after the tutorial).
Edit: A question by the way, if you fight the same enemies in the second part of a world that you did in the first, do they do increased damage? Because it feels like they do. (It's not my World Tendancy either I believe as it should have went back to what it was before I killed the first boss in Stonefang.)

I've playing a lot this week,. You're already farther in the game than I am. I think m soul level is 15 or so, and I still haven't beat any boss besides the first one,
Now that I've learned more on how to play, I love it. I had spent a good portion of the game not even knowing where to buy magic spells or miracles, Once II found the guys I jizzed my pants.Riposte is also pretty badass once you get the hang of it.
I spend most of my time hopping around from world to world, trying to get further in each, so I still haven't faced another boss. The dragon in world 1-2 is fucking me up right now, Can't get passed the bridge right after the underground tunnel.