United entered Sunday's match at a wet and windy Porirua Park knowing the equation was simple - win and fourth spot was theirs, lose or draw and it would be a sixth-placed finish.
Sara Eggesvik's powerful header in the 75th minute gave United the lead they were so desperately craving.
But just five minutes later Emma Main equalised for Wellington when she made contact with the ball while sliding in the box.
United's late attempts to snatch a winner fell short, meaning they will now take on third-placed Adelaide United away from home in an elimination final at Coopers Stadium next Sunday.
The other elimination final will feature fourth-placed Central Coast hosting fifth-placed Canberra United at Industree Group Stadium on Sunday.
Ladder leaders Melbourne City and second-placed Melbourne Victory earn direct entry to the two-legged semi-finals.
Wellington finish the season in ninth spot, but the come-from-behind draw at least sent off departing coach Paul Temple with something to smile about.
After the match, 33-year-old Phoenix midfielder Annalie Longo announced it was her final ALW appearance.
"It is the last game for me," Longo told Paramount.
"I'm proud of the performance.
"The energy in the second half was good. For Paul and myself, it's a full circle moment.
"I was lucky enough to be coached by him in the Under 17s in the World Cup for NZ. We've gone a long way, it's been a pleasure seeing him grow and develop as a coach."
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