The company's stock was slightly higher midmorning Thursday.
As of May 23, Berkshire Hathaway (BRK-A), Buffett's massive conglomerate, held a 14.88 percent stake, or more than 75 million shares, in Phillips 66 worth $6.17 billion, according to FactSet.
Phillips 66 shares are down about 1 percent year to date, but have fallen more than 10 percent over the past six months.
PSX 6-month chartSource: FactSet
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