The outspoken backbencher, who managed women’s refuges before becoming an MP, has been handed a key role in shadow home office team, focusing on domestic violence and safeguarding.
Ms Phillips, the MP for Birmingham Yardley since 2015, has won plaudits for her powerful speeches in the Commons, including her decision to read all the names of women killed by men in the last year every International Women’s Day.
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Ms Phillips initially stood against Sir Keir in the race to succeed Jeremy Corbyn but dropped out before the membership vote.
Her appointment came as the new Labour leader put the finishing touches on his shadow cabinet, with promotions for some MPs to the centre and the right of the party who languished on the back benches during Mr Corbyn’s tenure.
Liz Kendall, who came last in the leadership race in 2015, becomes shadow minister for social care, while Lucy Powell returns to the front bench as a shadow business minister after resigning in 2016 in protest at Mr Corbyn’s leadership.
Corbyn critics Wes Streeting and Stephen Doughty have also been promoted, as well as Pat McFadden, who was sacked by Mr Corbyn in 2016.
Ex-shadow international development secretary Dan Carden, an ally of Mr Corbyn, has been moved to the shadow Treasury team, while the former shadow culture secretary Tracy Brabin has been given a more junior post as shadow culture minister.
Angela Rayner, the party’s new deputy leader, also becomes shadow first secretary of state, which means she will deputise for Sir Keir at prime minister’s questions.
Rosena Allin-Khan, who came second to Ms Rayner in the deputy race, has been appointed as shadow minister for mental health.
Sir Keir said: “This is a new team that will take the Labour party forward in a new era.
“Under my leadership, the Labour party will be utterly focused on working in the national interest, rebuilding people’s trust in our party and winning the next election.”
Earlier in the week Sir Keir appointed Ed Miliband as shadow business secretary, moving his leadership rival Rebecca Long-Bailey, a close ally of Mr Corbyn, to the shadow education brief.
Annaliese Dodds, one of John McDonnell’s deputies in the shadow Treasury team, was named as the new shadow chancellor after Mr McDonnell stepped down.
Nick Thomas Symonds, the shadow solicitor general, was promoted to become shadow home secretary, and Lisa Nandy, Sir Keir’s other rival, has been made shadow foreign secretary.