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.

Phillips 66 shares are jumping 4% in intraday trading Tuesday following a report by The Wall Street Journal that Elliott Investment Management has built a more than $2.5 billion stake in the oil refiner.