Phelan has already selected his 30-man squad for the World Cup and the line-up that takes to the field in Caridff is likely to be the same to the one that will face England in the Pumas' first game in New Zealand on September 10.
It is the first game for Argentina, who finished third in the 2007 tournament, since facing a South American Select XV back in June and they will conclude their preparations for the World Cup with a fixture against English side Worcester Warriors next week.
Argentina 15 Martin Rodriguez, 14 Horacio Agulla, 13 Marcelo Bosch, 12 Santiago Fernandez, 11 Gonzalo Camacho, 10 Felipe Contepomi (c), 9 Nicolas Vergallo, 8 Juan Fernandez Lobbe, 7 Juan Manuel Leguizamon, 6 Julio Farias Cabello, 5 Patricio Albacete, 4 Manuel Carizza, 3 Juan Figallo, 2 Mario Ledesma, 1 Rodrigo Roncero.
Replacements: 16Agustin Creevy, 17 Martin Scelzo, 18 Mariano Galarza, 19 Alejandro Campos, 20 Alfredo Lalanne, 21 Nicolas Sanchez, 22 Juan Imhoff
Tickets priced at £20 for adults and £15 for under 18s are available at the WRU website or by calling the ticket hotlines 08442 777 888 or 02920 230130.
The buy one get one free offer applies across all ticket prices and ticketing outlets. Fans can visit www.wru.co.uk/tickets for more information.