You're on the right track.
Not too long ago I was walking along a nice residential street in my neighborhood. This kid appeared out of a pedestrian path that connected with another street. He behaved in a suspicious manner, and my inner alarms went off.
I reached for my cell phone and put it to my ear.
Immediately this kid started yelling at me about the fact I was on the phone. "Hey! Are you calling the police?" He got out of there pretty fast. He didn't get out his own phone. He just left.
Years ago I was working the grave yard shift at a convenience store. Two black guys pulled right up front and didn’t get out. A customer was checking out and I asked him to hang around and pointed out the two black guys. He advised me to pick up the phone and act like I was making a call. I did and the two guys left. Later that night 3 convenience stores were robbed.