Guillermo Mota allowed a leadoff single to Jayson Werth, and was lifted for Brian Shouse so that Shouse could face Chase Utley and Ryan Howard. (Charlie Manuel's refusal to always put a right-handed batter between those two is a big reason why the Phillies will have trouble winning a short series.) Utley sacrificed Werth to second, setting up Shouse versus Howard.
Yost elected to walk Howard to face Pat Burrell. This was... well, it strains my vocabulary to find the right word for it. Howard cannot hit left-handers, and would be a platoon player if performance mattered anywhere near as much as reputation does. Or if he had a competent manager. Howard is at .228/.313/.458 against lefties in his career, .212/.287/.410 this year. Howard. Can't. Hit. Lefties. Shouse, on the other hand, is in the major leagues for exactly one reason: lefties can't hit him, to the tune of .175/.192/.289 this year, and .211/.263/.325 for his career, which includes a bunch of years when he was barely a major leaguer. Manuel sending Howard up against Shouse was a continuation of a theme for the Phillies: not hitting for Howard when he has little chance of doing something good. He was giving Yost an out, and Yost gave it right back.
That set up Shouse versus Pat Burrell, which cried out for a right-handed reliever. After all, Shouse is a pure specialist (.307/.390/.455 vs. RHB career; .293/.371/.446 this year). The only way walking Howard even might make sense is if Yost were to bring in a righty to try and get a double play out of Burrell. Burrell doesn't have the big platoon splits he showed earlier in his career—he's a dangerous hitter against both kinds of hurlers—but leaving Shouse in to face him was asking for trouble.
Think about this for a second. Yost had a 481 OPS pitcher facing a 697 OPS hitter. He elected to issue an intentional walk in that situation to allow an 817 OPS pitcher to face a 905 OPS hitter with an additional runner on base. That's when you start looking around the roof of the stadium for snipers, because gunpoint is the only place where that kind of decision makes sense.
So it was no surprise that four pitches later, the Phillies were up 7-3. Burrell singled in one run, and Shane Victorino cleared the bases with a three-run homer to left.
If you're not going to let your left-handed specialist face Howard in that situation, when exactly should you be pitching to Howard? Moreover, if you'd rather have Shouse pitching to two good right-handed batters instead of bringing in one of your righty relievers, why not just release them all, because they're obviously not doing you any good. Eric Gagne, Seth McClung... none of these guys are very good, but all would have been better ideas than letting Shouse face Burrell. Heck, Todd Coffey is made for this situation, getting a right-handed batter out. For that matter, Salomon Torres could have been on the mound, but for the ridiculous idea of saving him for a save situation. Torres, the best righty the Brewers have, hasn't pitched since Wednesday, while Brian Shouse was facing righties with the game on the line.