I just got robbed

[Crazed Rabbit]

ACIN makes good points.

One thing I'll add: when shady people approach me asking for stuff, I will lie straight through my teeth at them. Never think you're under any obligation whatsoever to lend someone your cell phone or anything. It doesn't matter if they see you talking on it, don't feel obligated by what you think people expect. The simplest thing is just to say 'no'. Don't bother thinking up a reason or excuse. Say no, strongly, and keep moving (though keep an eye on them)

Importantly, you're alright and the phone was insured. Now, I'd suggest moving up the schedule for canceling the phone, changing bank account numbers, everything. Don't wait.

I think in this case (after you did agree to make the call) it would have been best to just start demanding he give you your phone back immediately after he grabbed it. Start loud and move to shouting quick - and then start yelling to the general public about stopping this 'thief' and yelling that someone should call the police. If he doesn't give it up, consider following at a safe distance.

EDIT: I'll just say that I agree with what Louis says in his own edit, the last paragraph.
This (NSFW: Swearing!) video illustrates the correct mentality. It's about a woman calling out the ass who tries to flash her on the subway.

CR