The incident occurred at around 8.30pm on Sunday 24 October in Market Square, Aylesbury.
The victim had their phone snatched from their hand and was grabbed in the throat and pushed by the offender.
Investigating officer Detective Constable Annabel Wilmot, based at High Wycombe police station, said:
“I would like to appeal to anybody who may have been in the area and witnessed this robbery to please get in touch.
“You can get in touch by either making a report online or by calling 101 quoting reference number 43210480419.
“Alternatively, for 100% anonymity, you can also call the independent charity Crimestoppers on 0800 555 111.”