As per molecular phylogeny is concerned don't rely on NCBI blast result. It is useful to get an idea of the specimen or its nearest neighbour but such estimation depends on the availability of correct sequences. There are many instances where people submit mislabeled or sequences from wrongly identified specimen. This can easily misguide your research. Moreover, there is every possibility that your sequences are the first to be submitted or in other words no similar sequences exists. In such scenario, proceed with the combined approach of morphology or classical taxonomic keys along with the genetic data.

All you have to do is that visit any good taxonomic literature to confirm your specimen's taxa like genus /species /family and so on or try to find its nearest neighbor taxa. Retrieve the sequences from the related taxa from NCBI (be sure to check the sequence length, publication status, geographic location or country/origin of the database sequence, etc.) and go for NJ clustering to see the clustering of your samples with the global dataset comprising maximum member of the taxa. In the subsequent step you can go for ML, MP or Baysian tree based on your hypothesis.