Houston is moving from a 4-3 front in which Williams had great success as a pass-rushing defensive end.
Williams has averaged over nine sacks every year since coming into the league in 2006, posting a total of 48 sacks in five years.
Much debate has raged on about whether or not Williams will have success moving from a hand-in-the-dirt rusher to standing up in Phillips' defense.
The central point of the naysayers' argument is that Williams will have too much of an adjustment period and won't be able to effectively drop into coverage.
Williams is a 6'7", 290-pound physical specimen who excels at making plays on quarterbacks.
What Wade Phillips sees is a DeMarcus Ware-like rusher with the capability to bring this defense to the next level.
Williams won't need to drop into coverage or go through an adjustment period to become a complete linebacker in this defense.
In fact, Williams' only conceivable purpose in the defense is to be a free-rusher and get after the passer.
Who will be the best fit in the Texans 3-4 defense?
Williams won't be asked to man-up against receivers, and he won't be assigned to zone coverage.
Mario Williams is going to be the free rusher that no one wants to block.
Giving the North Carolina State product a headstart at blockers by standing him up on the outside will only help him to make more of an impact.
The Texans had a great draft for their defense, getting a 5-technique in JJ Watt and a great outside linebacker in Brooks Reed.
Phillips figures to find a role for all of his players, and with Ryans and Cushing on the inside, the Texans will be stout against the run.
Now that they have Williams rushing the passer, the Texans can have success when teams drop back and throw the ball, too.
Houston made a good pick with Brandon Harris, and needs to give Harris a chance to succeed to early by giving him looks on the field.
Now that the Texans will have a better pass-rush, the team can test Harris in a low-risk/high-reward situation.
Obviously, despite the fact that Williams is a special pass-rusher, the Texans needed to make a change somewhere.
With Wade Phillips, they did just that.
The fact that Mario Williams is playing outside linebacker gives the team a much fresher outlook and gives them a free-rusher to match up with many other 3-4 outside linebacker stars.
The best-case scenario is that Williams becomes a preeminent enigma at the position, propelling the Texans to a Super Bowl berth and getting after Peyton Manning.
Also, Williams will get to Blaine Gabbert and Jake Locker early and often, only further perpetuating their propensity to have happy feet in the pocket.
The worst-case scenario is that Williams can't handle the change, and he moves back to the line.
Williams is a top defensive player, and is a fantastic candidate to be Wade Phillips' next DeMarcus Ware.
For a team like the Texans, this is the type of calculated risk that makes good teams great.
For Mario Williams, it's the next step for him to become on of the most dominant defensive players in the NFL.
Maybe a 6'7", 290-pound linebacker isn't so terrible to have lurking around.
Maybe the Texans aren't so wrong, after all.