Lalanne is replaced by Agustin Figuerola, while Bristol forward Mariano Sambucetti moves into the second row alongside Patricio Albacete.
"Before coming on tour, we decided to play some players who perhaps did not have too much experience of international rugby," said Phelan.
"We are not changing players because of performance. It is about what we think is best for this game against Wales. We think Wales will be very tough opponents - they are an excellent team that plays a very dynamic game.
"We saw them play New Zealand and Samoa recently, and also in the Six Nations this year. They are a good team that has played together a lot."
Argentina: Horacio Agulla; Lucas Borges, Gonzalo Tiesi, Martin Rodriguez, Mauro Comuzzi; Santiago Fernandez, Agustin Figuerola; Juan Fernandez Lobbe (capt), Alejandro Abadie, Tomas Leonardi; Patricio Albacete, Mariano Sambucetti; Martin Scelzo, Mario Ledesma, Rodrigo Roncero.
Replacements: Alberto Vernet Basualdo, Marcos Ayerza, Manuel Carizza, Alejandro Campos, Alfredo Lalanne, Benjamin Urdapilleta, Horacio San Martin