First the basics. Dominic is a 6'1", 205 lb Left handed hitter and thrower (as should be obvious from above). He's a High Schooler from the Los Angeles, CA area with a commit to play at USC. There's a lot to talk about here, almost too much, so let's get to it.
Technically a team could draft him to Pitch. A Mid 90's Fastball and above average Slider is a hell of a starting point for a Pitching prospect. No one's going to do that though. First off, he's way too good as a hitting prospect to get 4 or 5 plate appearances a week as a Pitcher. Secondly, scouts like big, projectable frames. Guys who are 6'3"+ get drafted as Pitchers. Outside of the occasional Tim Lincecum or Roy Oswalt there just aren't a lot of six foot starters and even those six footers who get drafted as starters get drafted behind a bunch of much taller guys traditionally. That's just how it goes. For these reasons I'm not going to spend any more time talking about Smith as a Pitcher (though I imagine he could have some succes there, and he'd quite possibly still be a top pick even as a Pitcher. LHPs capable of mid-90's don't grow on trees)
So, let's talk about Dominic Smith, the fielder first. He currently plays First base, though that seems like a waste for a kid with such a good arm. Second, Third and Short are out, since Lefties can't play those spots because of the need to turn and throw. Center Field is out because, while Smith isn't a lumbering oaf, he isn't athletic enough to cover all of the real estate in Center. That leaves 3 spots he could move to. Theoretically, you could try him at Catcher (he actually played Catcher some during the Perfect Game WWBA Tournament (it's a wooden bat tourney for 18 and under baseball prospects) this past year), but the risk of drafting a guy top 20 and teaching him the hardest position on the field both delays his time to the Majors and risks that his bat slips some while he focuses largely on defense. Many scouts seem to feel Smith is the best pure hitter in this draft, so put him in Right, hope he picks it up quickly, and Smith could be the rare High Schooler who moves fairly quickly through a system.
So, I've now mentioned he's a top hitting prospect, let's get into that part of his game. The first video below is courtesy of Perfect Game and is very recent video of Smith in game action. He has a bit of a leg kick, which I'm not a huge fan of, but several major leaguers use it and at the end of the day, if you can make it work for you, then it's a wonderful swing. It works for Smith, and it's not exagerrated. Second thing I noticed is how low and close he keeps his hand to the strike zone, allowing him to square up quickly on the ball. I like that a lot. Third thing I noticed is that he wiggles the bat in an almost Youkilis way. I have mixed feelings about that, though I'll admit it's mostly just a weird pet peeve with no reason to it. Smith draws a walk this at bat, but you get to see one hell of a mighty hack about 1:40 of the video.
Here's an older video courtesy of Bullpen Banter from last Year's Perfect Game All American Tourney. This video has everything, fielding drills in Right and at First, Batting Practice, Home Run Derby and game action. First thing you might notice in his hitting is that his stance seemed quite different in 2012. His hands appear to be higher, the bat wiggle is behind rather than in front of his head and his kick seems to be higher, while his stance is more closed. Though, in the game action, it looks closer to his more recent video. Also, he flat out rockets some balls in this video.
He's also widely regarded for his eye at the plate, as he walks at a good clip and rarely strikes out (though that likely will change as he faces better pitchers in the Minors, a 6% K rate just doesn't happen in the Majors or most of the Minors). Those are certainly promising signs.
What are the chances the Phillies can get this kid? Probably not great. Honestly, Smith could go #1 overall, but some mocks have had him drop, as teams may be scared off by the strong USC commitment combined with the harder slot that might make it tough to buy a kid out the way you used to. Combine that with his positional uncertainty (forget Pitcher, I'm talking First, Right, Catcher?) and maybe some teams decide they prefer other guys. So, while I think chances are slim he drops out of the Top 15, if he does, be very excited, as I expect Smith to be an even better prospect than Jon Singleton by this time next year. I like him that much.