The man entered Corner Phones on Teall Street on Sunday afternoon, May 29, shortly before 2pm and inquired about the white iPhone 13 Pro Max on display.
After quizzing the shop owner, Ebraheem Aljibori, about the phone and its storage capability, he then snatched it from his hand and fled.
Mr Aljibori said: "He said he wanted to pay for it on card and while I was dialling it up he just took it and ran.
"I chased after him and looked all over but I could not find him. I've never seen him before."
The man is described as being black and wearing a red baseball cap, dark zip-up hoodie and blue tracksuit bottoms.
Anyone with details should contact police on 101 and quote the crime reference number 13220293346.