At her best, Phillips is the Elvis Costello of female singer-songwriters: lyrically literate, harmonically adventurous, ornery, and original. Fortunately, Zero--a sampler from her four major-label albums with two new tunes--shows the L.A.-based popster (whose husband and longtime producer is T-Bone Burnett) at her best--literally. Why Phillips isn't yet a star is the major question left unanswered by this wide-ranging retrospective. A-