Providing verbal feedback to students is a great way to overcome the time/space gap inherent in online learning. Feedback that is frequent and personalized (to a degree tailored to the class size), has consistently proven to be an important component of many of the most successful online courses that I have reviewed.
Our institution uses the Canvas Learning Management System, and I encourage instructors to use the built-in audio recording tool for feedback. If your LMS does not have a built-in component, the open-source software program Audacity is very easy to use--and free :)
I think that hearing the instructor's voice creates an opportunity for a student to feel a deeper connection. It is also an efficient way to share feelings--curiosity, concern, empathy, etc.--that are difficult to represent in text. If you haven't used audio feedback in your online course designs, pilot it on a small scale, and see if you like the results.