They travelled to the AMEX Stadium full of confidence, with Brighton without a goal before kick-off.
However, Chris Hughton’s men found their groove and two goals from Pascal Gross put them in total control.
Tomer Hemed also scored for the Seagulls, before West Brom’s James Morrison found a consolation goal.
Tony Pulis’ men now sit ninth in the Premier League table and Phillips has conceded his team were just not good enough.
“It was difficult and we know we can play a lot better,” he is quoted as saying by the Brighton & Hove Independent. “We’ve got to dust ourselves down and get ready for next week.
“With the internationals, we’ve not had too much time to work on things but no excuses, we know we’re a lot better than what we showed today.
“There’s no easy games in the Premier League but we’ll work hard this week and go again this week.”