I am not sure what you mean by 6% to 22% homology.  Any two random strings of AGTCAGCGGTA are close to 25% identical without introducing any gaps to increase the alignment.  You must be referring to amino acid sequence identity.  Phages and other viruses do not have a typical Domain, Kingdom, Phylum, Class, Order, Family, Genus, Species ranking for many reasons.  They can be grouped into a similar sort of ranking but there are many places where this type of scheme does not work well due to recombination, entry and exit from host genomes, and other issues.

Many bacterial complete genomes in the databases are not annotated well, so there are many hundreds of phage genomes or partial genomes in the databases that will not be found very easily with a protein BLAST search.  Even DNA BLAST searches can easily miss many phages if the genome was not well assembled and resides in the short read archive or whole genome shotgun sequence repositories as dozens to thousands of short reads or small contigs, not fully assembled.  But even if you do find a match there, you end up with your unknown sharing x% sequence identy to some other unknown, and that may not be very informative.

Just to complement Brian's answer a little, I would say that, even for amino acid sequences, 6-20% of identity is an extremely low value for homologues, so please specify to what gene or protein sequence you were referring to with that range. If you were referring to whole genome alignment then the sequences were definitively not well aligned. I think you might want to look for a phylogenetic marker gene for your virus family instead. Also, please remember that when one deals with sequences one can only speaks of identities or similarities. Homology (or lack of) can then be inferred from there.. 

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