Activist investor Elliott Investment Management LP has built up a more than $2.5 billion stake in Phillips 66, and is looking for the energy company to either sell or spin off its midstream unit to help boost its stock price.

Elliott Investment Management said on Tuesday it has built a stake of more than $2.5 billion in U.S. refiner Phillips 66, and plans to push for operational changes as well as the sale of the company's midstream business.

Elliott Investment Management confirms a more than $2.5B stake in Phillips 66 and will seek to streamline the company, most notably with the sale or spinoff of its midstream business.