Phillips worked as UKIP's head of media for three years. Soon after the 2016 United Kingdom European Union membership referendum in which she voted for Brexit, she left UKIP, at around the same time as Farage, and in September joined the Conservatives, a few weeks after Theresa May had been elected as leader. She stayed on as a media advisor to Nathan Gill, a UKIP MEP and Welsh Assembly member who had become an independent in the Assembly after being beaten by Neil Hamilton for the position of group leader there. She explained her reasons for joining the Conservative Party as her admiration for then Prime Minister Theresa May's positions on Brexit, grammar schools, fracking, and the infighting within UKIP. In early May 2019, Phillips was announced as the Brexit Party's candidate for the South East England constituency in the European parliamentary election. A Green Party candidate also called Alexandra Phillips ran in the same constituency. Both were elected in the election. On 30 May 2019, less than a week after the election, Phillips appeared on the panel of the BBC's weekly Question Time, representing the Brexit Party. In July of the same year, Phillips admitted to working for SCL Group, the parent company of Cambridge Analytica, on Kenyan President Uhuru Kenyatta's successful 2017 re-election campaign. She had previously denied working for the company. Cambridge Analytica was a British political consulting firm that closed in 2018 after being found to have harvested millions of Facebook users' data without their consent for political advertising. The data was used to support the successful election of Donald Trump as President of the United States in 2016 and the company was also involved in supporting the pro-Brexit campaign prior to the 2016 UK EU membership referendum. In the European Parliament, Phillips was a member of the Committee on Development, and was part of the delegation for relations with South Africa. On 2 August, Phillips was selected as the Brexit Party's prospective parliamentary candidate for Southampton Itchen. However, on 11 November 2019, the Brexit Party announced that it would not stand in incumbent Conservative seats. The following day, Phillips announced that she would not be voting in the general election as she had been "disenfranchised" by her party. She was accused of having an affair with Nigel Farage by his wife https://www.thetimes.co.uk/article/farages-jealous-wife-wanted-ukip-aide-kept-away-cjcs76mw0