Sounds like some type of Melanoma; Acral Lentiginous Melanoma in my opinion. Hopefully this is localized and hasn't spread. Further investigation should be done to be certain this HASN'T spread. Ideally, this should be followed with lymphangiogram with lymph node dissection and/or chemotherapy after the digital amputation.
this opinion is only from a hand surgeon, would it be wise to see an oncologist for a second opinion
Definitely seek a second opinion on this; absolutely.