It happened between 6.10pm and 6.45pm on Monday, November 15.
The victim, a woman in her twenties, was walking along George Street towards the bus station, when the suspect barged into her from behind, causing her to fall.
The suspect ran off with the woman's phone through Leeds Outdoor Market and towards York Street.
He is described as black, about six feet tall and of athletic build.
He was wearing a zipped up black puffa jacket with hood, black slim fit jeans and dark trainers. He was also carrying a man-bag with a red strap.
Anyone who can assist this investigation is asked to contact Leeds District Crime Team on 101 or via the West Yorkshire Police website, quoting crime reference 13210590841.