The phone was taken after it's owner put it down on the counter at the restaurant at St James Retail Park in Knaresborough.
A North Yorkshire Police spokesperson said: "The incident occurred at around 4.15pm on Saturday, May 5, when the owner of the phone was reading the menu board before going to the back of the queue.
"While he was checking the menu he put his phone on the counter and forgot to pick it up. When he went back to the counter it had gone.
"CCTV from McDonald’s shows a man put the phone on his pocket before leaving."