The study of Lx phonology is under-represented in the GenSLA literature. I argue that this is largely because the complex learnability issues in the phonological domain have been under-appreciated. Drawing on examples from features and syllables, I illustrate that the acquisition of phonology is subject to poverty of the stimulus effects. Consequently, it follows that phonological representations are learned and not merely noticed in the environment. Furthermore, phonological grammars are shown to be generative, and hierarchical. By adopting abstract representational models we can both describe and explain learner behaviour. I explore the role of phonology in morphological and syntactic interfaces, and conclude with a discussion of real-world implications with regard to pronunciation training, and broader societal concerns.