Phenomena-based approaches have become popular for elementary school teachers to engage children's innate curiosity in the natural world. However, integrating such phenomena-based approaches in existing science courses within teacher education programs present potential challenges for both preservice elementary teachers (PSETs) and for laboratory instructors, both of whom may have had limited opportunities to learn or teach science within the student and instructor roles inherent within these approaches. This study uses a convergent parallel mixed-methods approach to investigate PSETs' perceptions of their laboratory instructor's role within a Physical Science phenomena-based laboratory curriculum and how it impacts their conceptual development (2 instructors/121 students). We also examine how the two laboratory instructors' discursive moves within the laboratory align with their's and PSETs' perceptions of the instructor role. Qualitative data includes triangulation between a student questionnaire, an instructor questionnaire, and video classroom observations, while quantitative data includes a nine-item open response pre-/post-semester conceptual test. Guided by Mortimer's and Scott's analytic framework, our findings show that students primarily perceive their instructors as a guide/facilitator or an authoritarian/evaluator. Using Linn's knowledge integration framework, analysis of pre-/post-tests indicates that student outcomes align with students' perceptions of their instructors, with students who perceive their instructor as a guide/facilitator having significantly better pre-/post-outcomes. Additional analysis of scientific discourse from the classroom observations illustrates how one instructor primarily supports PSETs' perspectives on authentic science learning through dialogic--interactive talk moves whereas the other instructor epistemologically stifles personally relevant investigations with authoritative--interactive or authoritative--noninteractive discourse moves. Overall, this study concludes by discussing challenges facing laboratory instructors that need careful consideration for phenomena-based approaches.