On the basis of a number of cases where the status of X with respect to phasehood changes depending on the syntactic context in which X occurs, I argue for a contextual approach to phasehood whereby the highest phrase in the extended projection of all lexical categories—N, P, A, and V (passive and active)—functions as a phase. The relevant arguments concern extraction and ellipsis. I argue that ellipsis is phase-constrained: only phases and complements of phase heads can in principle undergo ellipsis. I show that Ā-extraction out of an ellipsis site is possible only if the ellipsis site corresponds to a phasal complement. I also provide evidence for the existence of several AspectPs, all of which have morphological manifestations, in the VP domain of English and show that they crucially affect the phasehood of this domain. The article provides a uniform account of a number of superficially different constructions involving extraction and ellipsis from Serbo-Croatian, Japanese, Turkish, and English.