The former Manchester United and Real Madrid man was the inspiration behind the Galaxy moving into the MLS Western Conference final with a superb performance in midfield in the 2-1 win over Seattle Sounders which allowed his side to move through 3-1 on aggregate.
Beckham provided pinpoint crosses for both goals, which were scored by Edson Buddle and Omar Gonzalez, and his return to top form after months out with a serious Achilles injury was praised by Arena.
"His return from injury has been phenomenal, for him to be playing like this is fantastic," said Arena.
Beckham said it was a delight to be able to cross the ball having the knowledge that his teammates will be in good areas.
"I love putting crosses in and knowing that guys like Buddle will be there to get on the end of it," he said.
The Galaxy will take on FC Dallas in the Western Conference final on Sunday, November 14 with the winner taking going through to the MLS Cup final where they will meet the victorious team from the San Jose Earthquakes v Colorado Rapids Eastern Conference final.