Officials said Daniel So, 19, and Garrett Helstrom, 20, both of South Pasadena, are accused of robbing the man on Feb. 19 when he traveled to Temple City after arranging to pay $500 for the phone.
Upon meeting, So allegedly pulled out what appeared to be a semiautomatic pistol, took the victim's cash and fled on foot.
The victim was not injured.
An investigation by the Asian Gang Team of the sheriff's department led deputies to So's home on Friday, where they saw him get into a vehicle with Helstrom and drive away, he said.
Deputies found a replica of a semi-automatic handgun and suspected stolen property in Helstrom's car.
Both suspects were being held on $100,000 bail.
Officials said So and Helstrom may have committed similar robberies in the San Gabriel Valley.
The Associated Press and City News Service contributed to this report.