Argentina were focused solely on playing France in Lille on Saturday in the second of their November Tests.
The 38-year-old former international flank, who has been in his present role since 2008, said his side would need to have their wits about them up against one of the best teams in the world.
"We gained in confidence from the Wales win but now we have analysed this performance it is finished with," said Phelan, who guided the Pumas to the quarter-finals in last year's World Cup.
"We have forgotten Wales. We watched France play Australia [the French won 33-6].
"We know that we are about to confront one of the best teams in the world.
"The fact we have been together for three months has given us the best possible conditions to play them. When you have most of the players in the squad having been involved in the matches, that only serves to improve the spirit and the pride to wear the shirt."
Phelan, whose side drew a two-match home Test series with a largely inexperienced French side in the summer, said there were areas where his side needed to sharpen up on for the French encounter.
"In fact there are a lot of things we need to improve," said the 44-times capped Phelan, who captained the Pumas twice.
"Firstly we must continue to do what we did well against Wales.
"We know it will be a very competitive match. We must win a lot of possession. The difficulty for both Argentina and for France will be to win the ball and not turn it over."
Whilst Phelan is only too aware of the Pumas' excellent record against the French - they have won eight of their last 12 meetings - he knows that France at home and their crushing win over the Wallabies makes his side's task a tough one.
"We have often beaten the French but in June, in the second Test, France were clearly superior to us [they won 49-10]," said Phelan, whose side round off their European tour with a Test against Ireland on November 24.
"We also know what it means to be playing them in France, a country passionate about its rugby.
"We are preparing for the Test with that in mind, regardless of what happened before."
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