HOUSTON, March 26 (Reuters) - Activist investor Elliott

Investment Management has accepted the performance improvement

plan that U.S. oil refiner Phillips 66 laid out to boost

shareholder returns and share price, Chief Executive Mark

Lashier said in an interview on Tuesday.

"They've bought into our plans that we already had in

place," the CEO of one of the largest U.S. oil refiners said in

a briefing at its Houston headquarters.

Elliott sent a letter to the company's board last fall,

disclosing a $1 billion stake in the company, and calling for

additions to its board of directors and a focus on improving its

oil refining business.

(Reporting by Arathy Somasekhar)