"We are waiting to see if he gets the arm strength back and command of all his pitches and a little more sharpness with his pitches," Lehigh Valley manager Dave Brundage said.
The 6-foot-3, 228-pound Horst isn't throwing as hard as he did when he was called up by the Phillies on June 28, 2012. In 32 relief appearances, he was 2-0 with a 1.15 ERA, 40 strikeouts, and 14 walks in 311/3 innings.
"Obviously that was a good year, but that was a few years ago now, and to me it is not relevant to what I have to do now," Horst said.
That performance earned him a spot on a major-league opening-day roster for the first time, but he didn't have similar production. Horst had a 6.23 ERA in 28 relief appearances.
On June 16 he was placed on the disabled list with a left-elbow strain. After three minor-league rehab appearances, he was transferred to the 60-day DL on July 25 and missed the rest of the season.
Horst didn't need surgery, just rest.
"I just needed time for the tendinitis to get out," he said.
The inactivity and uncertainty were a challenge.
"It was frustrating, and it definitely was a lonely time," Horst said. "There is really nothing you can do but sit there and let your body heal."
Now he finds himself attempting to regain his form.
"Right now his stuff isn't like what it was a few years ago, but it is headed in that direction," said Joe Jordan, the Phillies' director of player development. "He needs the warm weather and the innings to kick up, but we still view him as a future major-league player."
Horst has taken a matter-of-fact approach to the situation in his return to the minors.
"We are down here for a reason, and everybody is working on things, and even guys in the big leagues are working on things," he said. "It's always a battle to better yourself."
Horst was a 21st-round draft choice of the Cincinnati Reds in 2007. He made 12 relief appearances for the Reds in 2011 (with a 2.93 ERA), but he was traded to the Phillies in January 2012 for infielder Wilson Valdez.
His brief time with the Reds and two stints with the Phillies have been invaluable.
"I know what the game is like up there, and I have seen it and been fortunate enough to have that opportunity, and every day here I come to work with an idea of what I need to improve on to give our club a chance to win," he said.
Horst doesn't want to dwell too much on the past, especially that 2012 season, but he obviously learned a lot about himself that year as a pitcher.
"It was a sign of my potential and what my abilities are," he said. "Do I think I can get back there? Absolutely."
And that is why he is using his time at triple A to regain his form, his confidence, and his footing in the Phillies organization.