A 47-year-old Bronx man was arrested yesterday for allegedly attempting to steal an iPhone from an undercover police officer stationed on a subway.The officer says Raymond Rodriguez tried to steal the device on the 4 train at Grand Central Station. In an attempt to decrease subway crime, the NYPD is doubling the number of decoy officers patrolling the system."They could be sitting right next to you, and they go in your pocket," one subway rider says. "If your phone was in your pocket, you're got. You've got to be precautious about things."Police are urging commuters to travel in groups, keep their electronics stored away and to sit in the conductor's car during off-peak hours.