In this article we explore the consequences of adopting recent proposals by Chomsky, according to which the syntactic derivation proceeds in terms of phases. The notion of phase – through the associated notion of spellout – allows for an insightful theory of the fact that syntactic constituents receive default phrase stress not across the board, but as a function of yet-to-be-explicated conditions on their syntactic context. We will see that the phonological evidence requires us to modify somewhat the theory of which functional categories actually define a phase. Patterns of default, syntax-determined, phrase stress are argued to result from prosodic spellout requiring the highest phrase in the spellout domain to correspond to a major prosodic phrase in phonological representation, and carry major phrase stress.