This qualitative-phenomenological study was directed to decode and examine the complexities of Mother Tongue-Based Multilingual Education (MTB-MLE) implementation in the transition stage particularly on the use of the target language as experienced by the grade four teachers in public elementary schools. Results revealed that teachers employed strategies such as translation, ICT aided instruction, language exposure and differentiated learning as viable means to address the problems they encountered on reading fluency, language proficiency, communicative competence and instructional challenges in using English as the medium of instruction. Furthermore, the study indicated that gradual bridging was vital to equip learners with the necessary literacy skills and knowledge for them to cope with the crucial transition and that further trainings were essential for teachers to be more effective in dealing with these multilingual learners. Hence, pedagogical implications of this study revolved around the complex transition vis-à-vis with the use of second language and the mandated MTB-MLE in the Philippine setting.