The Oracle of Omaha was asked outside of Berkshire Hathaway shares, which stock he would put all his money in today.
"If you look at our holdings, you would assume that we like them in the order in which they rank by dollar value of holdings, but if you look at them in terms of recent purchases over the last year we've bought more Apple than anything else," he said in a wide-ranging interview Monday on CNBC's "Squawk Box."
Buffett was also asked why he still uses a flip phone instead of an Apple iPhone.
"Tim Cook asked me that. Well the answer is just I'm out of touch. But I tell Tim, as long as I haven't gotten one the market is not saturated. The day I buy one, there is probably nobody left after that," he said.
Apple shares closed up nearly 2 percent on Monday.
He later explained why Apple is such an attractive investment.
"Apple has an extraordinary consumer franchise," he said. "I see how strong that ecosystem is, to an extraordinary degree. … You are very, very, very locked in, at least psychologically and mentally, to the product you are using. [IPhone] is a very sticky product."
Buffett shared Berkshire Hathaway's largest stock positions in his 2017 annual letter to shareholders released on Saturday and Apple is now the company's second-biggest holding.
Buffett said the company's interest in Kraft Heinz is not included on the list because Berkshire is part of a "control group" and must use a different method to account for its holding. He said the company's position in Kraft Heinz had a year-end value of $25.3 billion with a cost basis of $9.8 billion.
The investor also noted some of Berkshire's large stock holdings were managed by Todd Combs or Ted Weschler. He said each investment manager controlled more than $12 billion of capital each for the company.
Buffett also spoke on these topics in the CNBC interview:
— When choosing between stocks and bonds 'I would choose equities in a minute'
— I don't think Berkshire should avoid doing business with people who own guns
— The new GOP tax law benefits Berkshire and acts as a 'huge tailwind' for businesses
— There are three ways to go broke: 'liquor, ladies and leverage'