Phiri had a great debut last week as they beat Metz 3-1, but he knows that it will be a different ball game when they come up against Neymar and Co on Sunday afternoon.
The certificate has to arrive before Sunday if Neymar is to take to the pitch at the Stade du Roudourou this weekend, with it possible that Federation Internationale de Football Association may have to intervene if the RFEF do not send the document by Friday.
"He's been working well and we looked hard at tactics and free-kicks", said the Spaniard.
That figure has been reduced over the course of various appeals from Neymar's camp, who have calculated the £1.9m figure they believe will wipe the slate clean.
You've got a £50m budget to pick 11 players, with all the biggest new signings ready and raring to go ahead of a mouthwatering new Premier League campaign. "Players today move to where they're wanted the most", Xavi told Le Parisien.
It was reported Neymar Sr held up the deal in order to trigger a loyalty payment that would be owed after July 31, as part of the new contract the player signed with the Catalans last October.
Hence, the Barcelona boss has been left scrambling in search of a top replacement for Neymar.
The lawyers of the two clubs complete great deal which will soon receive official confirmation.
Despite spending some downtime relaxing with his team-mates, Neymar will be eager to make his debut and impress his new supporters.
Barca's scattergun approach to finding a replacement for Neymar has so far been unsuccessful with bids for Liverpool's Philippe Coutinho and Ousmane Dembele of Borussia Dortmund rebuffed.
Madrid too have been linked with the 18-year-old, who scored 26 goals for Monaco in his first full senior season, helping the principality club win Ligue 1 and reach the Champions League semi-finals.
It was understood Neymar opted for Unai Emery's side to break clear of Lionel Messi's shadow and lead the line but whatever the line-up, a combination with Mbappe up front will undoubtedly form one of the most deadly strike forces in football.