The Labour MP defied her party leader by voting for an SNP motion calling for an immediate ceasefire in Gaza.
Sir Keir had signalled before the vote that MPs holding frontbench roles would be sacked if they backed the ceasefire call.
Announcing she was quitting her role as shadow domestic violence minister, Ms Phillips said she was voting with “my constituents, my head, and my heart”.
Ten of the party’s frontbenchers have left their jobs over the vote, including eight shadow minsters.
