It's hard to pick the top album because I have two competing criteria. In terms of the number of tracks I enjoy, NJR wins (love Inside Out, We Said Hello Goodbye, Take Me Home, etc.). In terms of ground-breaking and most "Genesis-like" I go with Face Value.
I think that one aspect of Phil's solo albums is that they're about as far from Genesis as you can get! Face Value being no exception to that - indeed, at the time of that record's release I think Phil would have been most distressed to hear anyone describe his efforts as being "Genesis-like"!