This paper reports on a phenomenographic study investigating former grade 12 STEM students' conceptions of online learning during COVID-19 pandemic. Purposive sampling was employed in selecting participants who were enrolled in a private school in Laguna, Philippines that formally implemented a fully online learning setup for SY 2020-2021. By using semi-structured interviews, results conveyed an outcome space comprised of nine (9) core categories of description: (1) online learning marred with unfavorable sentiments; (2) online learning plagued by technical barriers; (3) online learning accentuated the use of online tools; (4) online learning provided aberrational learning experiences; (5) online learning hampered by the learning environment; (6) online learning adversely affected students' wellbeing; (7) online learning reaffirmed the importance of social interactions; (8) online learning exhibited unsatisfactory perceptions to teaching; and (9) online learning exhibited dissatisfaction towards institutional support. Within each core category, a variety of subcategories fulfilled the anatomy of experience and describing the complexity of the relation between STEM students and online learning during COVID-19 pandemic. Analysis of all core categories of description revealed a generally unfavorable and unenthusiastic view of online learning during COVID-19 Pandemic, with 'online learning provided aberrational learning experiences' as the most prominent core category of description, emphasizing how the deviation from the normal setup adversely affected their learning experiences. Findings revealed in this study can be beneficial in formulating future policy changes and bases of interventions to improve the conduct of online learning and provide a more effective pandemic response in the educational system. [This manuscript was presented in the ASAA Conference 2022, last July 6-8, 2022.]