Unfortunately commonplace in Barcelona. A thief that is caught will only get a small fine for thefts under 400€ even if it's the 1000th time. So the chance of a fine is just taken as the cost of doing 'business' by these professional pickpocketing gangs.
If there's violence involved it's another story but if a victim initiates it, they themselves can get into trouble. So these thieves are trained to be ultra passive.
That's probably the best time to steal it: the device is unlocked, giving access to the data and settings etc. Also the owner is distracted looking at the screen, and it's held in a position conducive to snatching. In short I'd expect this to be the main mode of phone theft directly from the owner.
It's a fairly common tactic in the UK. I've seen plenty of CCTV clips where kids cycle past people on their phones and snatch them. The thief is 10m away before the person's even reacted.
