Labour will need a “big personality” if it is to win back the millions of voters it lost at the election, Jess Phillips has said, as she joins an increasingly crowded field competing to succeed Jeremy Corbyn as party leader.

With Lisa Nandy and Sir Keir Starmer also declaring their candidacies this weekend, Phillips, the outspoken MP for Birmingham Yardley, says modern politics demands a blend of passion, energy and belief rooted in experience, which she believes she possesses.

“I’m not so arrogant that I believe my personality alone will transform our fortunes,” she writes in today’s Observer. “And I know that sometimes my passion gets the better of me.

“But who you are, where you come from and what you care about matters. Politics has shifted in a fundamental way. All over the world we see that it isn’t enough to offer big change, you also need a big personality.

“I’m standing as leader because I believe I can combine the energy and activism of the last few years with an ability to speak in a language that shows our lost voters that we get it, that we care, that we are back as their party. That’s how we begin to give people hope again.”

Emily Thornberry, the shadow foreign secretary, and Clive Lewis, the MP for Norwich South, have already declared they will stand in the contest, which is expected to conclude in late March, while Rebecca Long-Bailey, the shadow business secretary, is expected to do so soon.

On Monday, Labour’s national executive committee (NEC) will meet to decide the timetable and rules for the race, including a cut-off point by which Labour supporters must have joined the party as full members or registered supporters in order to vote.

It is likely that the contest will run for 12 weeks, concluding before the party launches its official campaign for the May local elections. In order to get on to the ballot paper, contenders first have to gain the backing of at least 10% of Labour MPs and MEPs, and reach a separate threshold of support from constituency labour parties or organisations affiliated to the party, including unions.

In her article, Phillips makes clear that she will put her personal story, as the daughter of two public sector workers in Birmingham – her father was a teacher and her mother as a manager in the NHS – centre stage.

David Lammy has decided not to run, saying that, as an ardent Remainer, he is not the candidate best suited to bringing the party together. Photograph: David M Benett/Getty Images

“For me, socialism has never been an intellectual pursuit,” she writes. “It comes from my upbringing and experience. The stories retold in my family were of my mum chasing a racist distributing National Front leaflets out of our street. Or my nan, a fearless dinner lady, sitting beside an Asian man on the bus who was being racially abused. I was taught if you have a voice, you use it to help others.”

Nandy, the MP for Wigan, has also emphasised the need for a strong personality, one who could reconnect with Labour’s lost supporters.

“The situation we’re in requires a different kind of leadership and that means a different kind of leader,” she told the Observer. “Our members need to be listened to. They’re the ones who have been out knocking on doors and speaking to people – so they knew this was coming and now they need to be heard. That’s why I will be travelling the length and breadth of the country over the next few weeks to see the best grassroots projects our activists are leading in their communities, and to hear from them and the public about the lessons we need to be hearing if we are to win back people’s trust.”

Starmer launched his campaign on Sunday, stressing that the party must not abandon the radicalism of Corbyn’s leadership but that it needs to restore people’s trust following a disastrous showing. “We need a Labour government that will offer people hope of a better future,” he told the Sunday Mirror. “However, that is only going to happen if Labour listens to people about what needs to change and how we can restore trust in our party as a force for good.”

David Lammy, the MP for Tottenham, ruled himself out of the contest on Saturday. The former minister said he had decided not to take part after “serious consideration” and having concluded that, as an ardent Remainer, he would not be the candidate to bring the party together.

“A key role, however, for the next Labour leader is to win support from, and foster unity between, different vociferous factions of our party, so that we can win back the trust of our country,” he said. “I am not the individual best placed for this role at this time.”

Once the contest is under way, the candidates will hold a series of hustings at Westminster and across the country as they seek to win the necessary support to move to the voting stage. Full party members, registered supporters and affiliated supporters will then be able to cast their ballots either online or by post. There will be a separate, parallel contest for deputy leader, following the decision by Tom Watson to step down before the election.

Labour leadership Q&A

Who are the contenders?

There are six candidates who have either declared their intention to stand, or who seem likely to do so by early this week. They are: Emily Thornberry, Clive Lewis, Jess Phillips, Lisa Nandy, Keir Starmer and Rebecca Long-Bailey. Others, including Yvette Cooper and Ian Lavery, may yet do so.

Will those who declare all get on the ballot paper automatically?

No. They need to meet a series of thresholds to do so. To reach the final stage, they must first win the backing of 10% of the 212-strong cohort of Labour MPs and MEPs. And second, they have to be nominated either by at least 5% of the 647 constituency Labour parties (CLPs) or at least three organisations affiliated to the Labour party (two or more of which must be trade unions affiliated to the party).

Once the successful candidates have got on to the ballot paper, what happens?

Before 2014, the eventual leader was chosen by an “electoral college” in which MPs, the unions and other affiliated organisations, and members had a third of the vote each. The system was abolished by former Labour leader Ed Miliband and it is now a one-member-one-vote arrangement. Candidates will hold numerous hustings before forms go out and voting begins.

Who exactly can vote?

There are three categories. The first is full members of the Labour party (around 500,000). The second is affiliated supporters who are members of unions or socialist societies who opt-in to the process. Just under 100,000 took part through this route in the 2016 contest. The third is registered supporters who pay a reduced fee that gives them the right to vote in leadership and deputy leadership contests; 120,000 of these voted in the 2016 contest.

Can people still join now in order to have their say in who succeeds Jeremy Corbyn?

Yes, but there will be a cut-off point from the moment the contest starts. The national executive committee (which meets to finalise the rules and timetable tomorrow) is expected to decide that anyone wanting to vote must have signed up as a member or supporter within a fortnight of the contest being triggered.

When will the new leader be anointed?

Normally contests take about 12 weeks but there is pressure from Labour councillors to complete this one quicker so the party can have its new leader in place well before campaigning starts for May’s local elections. The new leader will almost certainly be in place before Easter (12 April).