Which Boeing type are we talking about?
On the 737 the initial sequence is made of three steps which are Thrust Lever -> Speedbrake -> Reverse as galdian correctly pointed. A two step maneuver would stress the hardware beyond it certification limits. This is also valid for 744s, 767s and 757s. Refer to Boeing FOT 737-13-1 or their equivalent for other types. The No Technical Objection previously granted by Boeing to use a two step maneuver on those types is no longer valid.
On 777 and 787 the two steps sequence is Thrust Lever -> Reverse and you only have to verify the Speedbrake automatic extension. Those types are the only for which Boeing approves a two step maneuver.
Hope this helps. Flew both 737 and 777.
PG