Native English speakers were instructed to detect instances of /√p/ in spoken sentences by pressing a button as soon as they hear /√p/ regardless of whether it is inside another word. We observe that detection of the particle up is slower when the frequency of the verb+up collocation is low or extremely high than when it is medium. In addition, /√p/ is more difficult to detect in high-frequency words than medium-frequency or lowfrequency words. Thus word frequency has a monotonic effect on detectability of word parts while the effect of phrase frequency is U-shaped. These results support the hypotheses that lexical units compete with their parts during speech perception and that words and ultra-high-frequency phrases are stored in the lexicon.