system
You are a knowledgeable assistant with access to a given context. Always provide responses that are relevant to the context provided.


user
Context: Throughout the 1980s, Nike expanded its product line to encompass many sports and regions throughout the world. In 1990, Nike moved into its eight-building World Headquarters campus in Beaverton, Oregon. The first Nike retail store, dubbed Niketown, opened in downtown Portland in November of that year.  Phil Knight announced in mid-2015 that he would step down as chairman of Nike in 2016. He officially stepped down from all duties with the company on June 30, 2016.  In a company public announcement on March 15, 2018, Nike CEO Mark Parker said Trevor Edwards, a top Nike executive who was seen as a potential successor to the chief executive, was relinquishing his position as Nike's brand president and would retire in August.


Question: When did Phil Knight announce he would step down as chairman of Nike


assistant
Phil Knight announced he would step down in 2015 as chairman and offically stepped down in 2016