The 22-year-old was a key player for Mexico in South Africa and scored twice for his country.
“We were quietly pleased with what we saw of Javier at the World Cup,” Phelan told the club’s official website.
“He is still on a break but we would like to get him on board as quickly as we can, so he will join us in America. Then hopefully he will be a major influence on the team.
“We did the deal before the World Cup and that has probably helped us a little bit! He has only just begun his career with the national team but already he is a very influential player for Mexico.
“He is young, athletic and as keen as mustard. He will be a good addition.
“We all hope he hits the ground running and adds to what we think is a good blend of youth and experience in our squad. We just hope it all comes together.”