Activist Elliott Investment Management on Tuesday disclosed a stake in Phillips 66 valued at more than $2.5 billion and said it is pushing the oil refiner to consider operational changes to boost its stagnant stock.

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 has reportedly acquired a stake exceeding $2.5bn in Phillips 66 and plans to advocate for operational changes, including the sale of the company's midstream business. The news has seen Phillips 66 shares rise by 3.