Bernstein analyst Toni Sacconaghi said in a note to investors on Friday that people are holding on to their iPhones longer than ever before, which may spell trouble for Apple as consumers upgrade to new models less often.

"Replacement cycles are elongating ... a lot," Sacconaghi said, noting that people are using their iPhones longer because of Apple's battery replacement program, changes in carrier subsidies and higher prices, among other reasons.

Apple CEO Tim Cook confirmed this on a company earnings call last month.

"Our customers are holding on to their older iPhones a bit longer than in the past," Cook said. "When you paired this with the macroeconomic factors particularly in emerging markets, it resulted in iPhone revenue that was down 15 percent from last year."

Sacconaghi said 16 percent of that base will buy a new iPhone this year and that Apple's fiscal 2020 "offering is unlikely to stimulate an acceleration in iPhone replacement cycles."