(CNBC) The prospect of slowing iPhone sales later this year limits the upside for Apple’s stock, one tech analyst said Tuesday. In the final quarter of last year, the tech giant sold a record 74.5 million iPhones. With a “really tough” comparison for the device, Apple faces a “very real possibility” of negative year-over-year sales, said Abhey Lamba, senior technology analyst at Mizuho Securities.