The Birmingham Yardley MP did not attend the latest hustings, by the GMB, in London today.
She had not been expected to win the union’s backing but she is believed to have been struggling to win support as many party members opposed to another Corbynite candidate are swinging behind Sir Keir Starmer.
Frontrunner Sir Keir last night became the first candidate to get onto the leadership ballot after landing the endorsement of the Usdaw union.
Left-winger Rebecca Long-Bailey is expected to follow suit when Unite meets on Friday.
Neither Ms Phillips nor other contender Emily Thornberry, who set about garnering backing through a number of interviews today, are tipped to be endorsed by any of the big five trade unions.
This means they will need considerable support from local party branches to avoid elimination.
Supporters of Lisa Nandy were hoping she would get the endorsement of the GMB union today.