Phasing: If the reference sequence assembly is reasonably complete, it may be possible to map the variant calls to a consistent strand. The term for this is phasing. A VCF file may be completely un phased or each call can indicate phased or unphased. The degree of completeness depends on how well and how unambiguously the calls map to the reference.
Filters: FILTER is one of the standard VCF columns. Valid values for FILTER column are "PASS" or a code for the filters that the variant call fails.