The legendary American swimmer competes in his first international event since coming out of retirement when he races in Australia this week.
Phelps failed to win any of his four events on his comeback at the US National Championships earlier this month and admitted he found it hard to accept failing to win.
The 29-year-old 18-time Olympic champion will race in the 100metre freestyle at the Gold Coast Aquatic Centre on Friday, then also line up in the 100m butterfly, 200m medley and possibly also races in relays.
And Phelps is determined to cut out the errors as he gears up to competing in the World Championships in Russia next year and the 2016 Rio Olympic Games.
Phelps said he was "kind of rusty on judging the speed going into my walls," and his turns were "awful" as he continues to set the highest standards for himself.
"Those were the big things that I guess I forgot how to do," he said at a press conference on Wednesday.
"Not winning, it is what it is - I hate to lose - but I always do understand it's not going to come back instantly.
"I would rather have those instances now than farther down the road. World Championships is next year...Olympics the year after that. Hopefully I'll be able to fix the things now."