The record 22-time Olympic medallist came out of retirement earlier this year, but his return to the pool has not entirely gone to plan.
Phelps was second in the 200 metre freestyle at the Arena Grand Prix before finishing seventh in the 100m freestyle final at the US National Championships. He also had to settle for second in the 100m butterfly final and individual medley.
The Pan-Pacific Swimming Championships, which takes places in Australia and starts next Thursday, is next up for 29-year-old, who insists he is not looking too far ahead.
"I don't even know what I'm swimming next week so I'm not sure what the future will hold," said the American.
"I will say I'm not swimming eight [Olympic events] again. That is a safe thing to say."
Following two years out of the sport, Phelps acknowledges it will take time to rediscover his spectacular form of old.
"This is all really a stepping stone," he added.
"The biggest thing about this summer is getting on the team to hopefully propel me for next year and then move forward from there.
"Step one is complete by making this team and now we have some other things to do next week and hopefully we can do those and propel ourselves into next season."
Meanwhile, team-mate Ryan Lochte - who edged Phelps to the 200m individual medley title at the US National Championships - admits he is delighted to see his rival back in action.
"I think after London [2012 Olympic Games] when he [Phelps] said he was announcing his retirement I think I was the only one who said 'no', it wasn't going to happen.
"I think I was the first one to say 'He's going to come back'. Once you have that competitive edge in you its hard to get rid of.
"Like he said, he missed it. He missed being in that water, getting up on those blocks and the excitement of racing the top guys in the world. He missed it and that's why he came back. And now he's having a lot more fun than right before he retired so I'm glad he's back on the team and representing the USA."