The 29-year-old woman was walking along Back Hatfeild Street in College Grove, Wakefield, at around 1am on Tuesday, August 11.
She was approached from behind by a man who asked her for the time.
The victim then tried to walk away but the man grabbed her shoulder and took her mobile phone from her back pocket.
As she tried to stop him the suspect then punched her in the face, causing her to fall to the floor.
The woman was left with facial injuries as a result of the assault and detectives have now released an e-fit image of a man they would like speak to in connection with the incident.
He was described as white, with tanned skin, in his mid 30s 6ft tall of average build, mid 30’s and as having short dark hair.
He was wearing a dark coloured hooded top and dark bottoms, had the hood down and spoke with a local English accent.
Det Con Mark Hargreaves, of Wakefield CID, said: “This was a serious incident in which the victim has been left with facial injuries after being followed and then assaulted by this man.
“I would like to hear from anyone who recognises the man in the e-fit, saw a man fitting this description in the area at the time of the offence or has any information which could help us identify him.”
Anyone with any information should contact Wakefield CID on 101 or Crimestoppers, anonymously, on 0800 555 111.