The right-hander, who was called on to pitch in the inning with the Brewers trailing 8-5, first vomited behind the mound after finishing his warm-up tosses. Manager Craig Counsell came out to the mound and gave the pitcher a bottle of water while the grounds crew came on to clean up the spot. He then threw a few more warm-up tosses and remained in the game. He allowed a double to Phillies catcher Jorge Alfaro to open the inning and then got pinch hitter Jesmuel Valentin to ground out before vomiting a second time.
Counsell came back out of the dugout to check on Houser again, but the pitcher was able to remain in the game. He allowed a run-scoring double by shortstop Scott Kingery but then got second baseman Cesar Hernandez to fly out and left fielder Rhys Hoskins to ground out.
The Brewers were not charged with mound visits when Counsell checked on his pitcher, umpire Laz Diaz indicated on the field.
"For Adrian today, it was just kind of a combination of a bunch of factors. He wasn't under the weather at all, but it was an early wake-up call, not enough food, heat, probably a little nerves from getting to the big leagues today," Counsell said.
"There wasn't very much coming out. It wasn't a food thing," he said with a chuckle.
Counsell, who played 16 seasons in the majors and has been the Brewers' manager since 2015, said this was the first time he saw a pitcher vomit while on the mound. He said he wasn't worried about Houser's safety.
"Adrian was completely fine," Counsell said. "It was like he was just trying to get that part over with. There was no panic in his eyes, not in any way. He was talking and he wasn't struggling at all. Like I said, it was just a kind of combination of all those factors. He was fine, kind of after he sat down and everything was good."
This was just Houser's fifth major league appearance. He had made two appearances for the Brewers in 2015 and two this season before Sunday.
"I think it was a combination of traveling this morning and not having a lot of food in me. I was trying to stay hydrated in the bullpen. It's pretty hot here compared to Colorado Springs. All combined, it got me," Houser said.
Houser's willingness to stay in the game impressed Phillies manager Gabe Kapler.
"I have a lot of respect for anybody who would step behind the mound and throw up and step back on the mound and pitch,'' he said.
Houser was recalled from Triple-A Colorado Springs earlier Sunday. The Brewers optioned right-hander Jorge Lopez to Colorado Springs in a corresponding move.
The Associated Press contributed to this report.