Hi Victoriaenglish,
"Mob" means an unruly and agitated crowd. When you "get mobbed", you are surrounded by such a crowd. Perhaps you touched a raw nerve of a taxi driver. Very soon, other taxi drivers were drawn into the dispute as they felt the same indignation (perhaps people of the same profession have similar experiences and react similarly to a situation).
You may use the phrase to refer to a riot, a group of paparazzi or a group of supporters.
Hope this helps.
Cheers,
Lance