Office hours are an integral component of science, technology, engineering, and math (STEM) courses at nearly all colleges and universities. Despite their ubiquity as a support mechanism, there has only been limited work examining how instructors approach office hours and what shapes these approaches. Here, we conduct a phenomenographic study to investigate how instructors of STEM courses experience office hours and how these experiences may impact their approaches to promoting and managing office hours. We identified variations in how instructors promoted office hours, the modality of office hours (i.e., when and where office hours were held), and how instructors facilitated learning during office hours. These variations spanned from student-centric (strategies instructors use with students' interest in mind, e.g., wanting to increase student learning, accessibility, comfort, etc.) to instructor-centric (strategies the instructors use with their own self-interest in mind, e.g., saving time and/or bandwidth, personal needs, comfort, etc.). Additionally, we identify several challenges and barriers, including a lack of formal training or opportunities to discuss office hour approaches with other faculty, and conclude with general recommendations for instructors and administrators in STEM departments for engaging and supporting students during office hours.