Voice Assistants (VAs) present promising opportunities for the development of applications for the work domain. While previous research is primarily focused on aiding groups and individuals to be more productive, studies exploring the use of VAs to train and develop collaboration skills are rather limited. In this paper, we examine whether VAs can be used to help individuals improve their collaboration skills through self-reflection. We developed ReflectPal, a Google Assistant application designed to facilitate reflection sessions regarding collaboration challenges. First, we identified a list of frequently occurring challenges in a specific collaboration work environment. Then we designed ReflectPal to address a subset of those challenges and tested it in a two-week in-situ deployment with 19 participants. We found that participants benefited from the structure that the practice provided, leading to deeper and more meaningful reflections than before. However, the study also highlighted the need to design applications that take motivational aspects into account to encourage frequent engagement in self-reflection for skill development. Reflecting on insights from our study, we discuss future design directions of VAs for facilitating self-reflection in a collaborative work context.