Barreto enjoyed a two-week stint with the A's earlier this summer when second baseman Jed Lowrie was out of action, batting .190 with two home runs before returning to Triple-A Nashville. Barreto responded by batting .304 with seven home runs in his final 43 games with the Sounds, including .349 in August.
The 21-year-old middle infielder is expected to get a start in Seattle this weekend, as the A's plot out his playing time for the month.
"But obviously being our No. 1 rated prospect, it's a guy you don't want to sit around a long time," A's manager Bob Melvin said.
Barreto said through team interpreter Juan Dorado that he'd like to work on slashing his strikeout numbers. He had 18 of them in 42 at-bats during his first stint with the A's.
"I want to show them that I have a better eye at the plate, better at-bats, not strike out so much," Barreto said. "I'm really happy to be back. I'm really grateful to the team for giving me an opportunity to be back."
Moll, acquired from the Rockies on Aug. 16, did not allow a run in seven innings with Nashville, after posting a 4.18 ERA in 44 appearances for Colorado's Triple-A affiliate -- prompting the Rockies to designate him for assignment.
The left-hander made his big league debut with two outs in the eighth inning Friday, making quick work of Yonder Alonso, who flied out on the second pitch he saw from Moll. The pitcher had his fiancé, parents and several friends in Seattle for the occasion.
"It was good to get in there and get some work on the first day" Moll said. "I didn't really feel too nervous. I think I maybe only threw one strike out of eight warmups out there, but I felt pretty comfortable for that first one, as comfortable as you can."
The left-hander, giving the A's two in their bullpen, isn't just good for a left-on-left matchup; he can go multiple innings, too.
"Looking at the numbers, he's done a nice job since he's been here for us," Melvin said. "About as good as you can get."
For Smolinski, his latest opportunity with the A's is just as much of a reward for working his way through a grueling rehab process after undergoing right shoulder surgery in March. The outfielder, who is still getting through a throwing program, will be limited to hitting and running duties until the middle of the month.
"It's a little against the grain to have a guy who can't play the outfield, but for a guy that worked as hard as he did, is well liked around here, he can give us some DH at-bats, pinch-run and stuff like that," Melvin said. "It's nice to have him here and see a smile on his face, because he's had a pretty tough summer."
Smolinski hit .182 in 13 rehab games and left open the possibility of playing winter ball to get more at-bats under his belt.
"Just trying to get back in the swing of things with hitting," he said, "but it's great to be in the clubhouse on the road, see my name on the card. It's good to be back."
Phegley, meanwhile, is returning from a left oblique strain, giving the A's three catchers on their roster. More additions are expected when Nashville's season ends Monday, including power-hitting corner infield prospect Renato Nunez.