First phoneme queries are important functionalities that provide an improvement in the usability of interfaces that produce errors frequently due to their restricted input environment, such as in navigators and mobile devices. In this paper, we propose a time-space efficient data structure for Korean first phoneme queries that disassembles Korean strings in a phoneme-wise manner, rearranges them into circular strings, and finally, indexes them using the extended Burrows-Wheeler Transform. We also demonstrate that our proposed method can process more types of query using less space than previous methods. We also show it can improve the search time when the query length is shorter and the proportion of first phonemes is higher.