Warren Buffett is still a big believer in Apple.

The Oracle of Omaha was asked if he bought more shares in the technology giant after the end of the June quarter. Buffett's Berkshire Hathaway increased its stake in Apple by 5 percent in the second quarter, according to a 13F regulatory filing.

"We bought just a little [more]," he said Thursday on CNBC in an interview with Becky Quick.

Earlier this month, Apple became the first publicly traded U.S. company to reach $1 trillion in market value. Berkshire Hathaway is the second-largest holder of Apple shares with a stake worth about $56 billion, according to FactSet.

Buffett explained that he loves Apple as an investment due to the power of its brand and ecosystem, not its short-term financial results.

"I do not focus on the sales in the next quarter or the next year," he said. "I focus on the ... hundreds, hundreds, hundreds millions of people who practically live their lives by it [iPhone]."

He also called the iPhone "enormously underpriced," saying that it's worth far more than the $1,000 Apple charges.

"I have a plane that costs me a lot, a million dollars a year or something of the sort. If I used the iPhone -- I use an iPad a lot -- if I used the iPhone like all my friends do, I would rather give up the plane," he said.

"Now it's got competition so you can't push the price, but in terms of its utility to people and what they get for a thousand dollars...you can have a dinner party that would cost that, and here this is, and what it does for you, it's incredible."

The billionaire investor spoke with CNBC on his 88th birthday from the Smith & Wollensky steakhouse in New York, ahead of his lunch with the winning bidder of the Glide auction.

The annual event raises money for the San Francisco charity by offering a private meal with the Berkshire Hathaway chairman and CEO. This year's winning bid went for over $3.3 million.

Watch the full Buffett interview here.