Hi @Aaron P
As of now, there is no direct graph API endpoint available to get contact groups (contact lists) for outlook user accounts. Microsoft provides API endpoints for listing contacts and listing contact folders, but this does not list contact groups.
So I recommend that you submit a user voice to add a support request for the feature, and I will upvote for you to increase the priority of the request.
If the answer is helpful, please click "Accept Answer" and kindly upvote it. If you have extra questions about this answer, please click "Comment".