This paper attempts to verify the theoretical claims in Syntax ($Bo{check{s}}kovi{acute{c}}$ & Lasnik, 2003; Kim, 1999, 2004) about the phrasing in English that-clauses, presenting an acoustic experiment conducted to observe the patterns of edge tones at the boundaries of that. In the experiment, two different that clauses, complement and relative clauses, were varied in forms (that-retention, that-deletion, adverb insertion before that) and length. Results showed that edge tones, if occurred, mostly showed up before the complement clauses in that-deletion sentences (67%), and that their positions polarized in adverb insertion sentences (56% before toot and 44% after toot). In the relative clauses, phrasing mostly occurred before toot as opposed to after toot in that-retention (73%) and adverb insertion sentences (87%). Additionally, phrasing tends to occur more frequently as the sentences get longer. The results suggest that the previous claims based on syntax are not consistent with the results of the current phonetic experiment. This may be interpreted as stating that syntactic boundaries do not always indicate phonetic phrasing, and that there may be some other factors to determine phrasing patterns, for example, rhythmic phrasing operating at the surface level of speech.