Flot (2010) SeqPHASE: a web tool for interconverting PHASE input/output files and FASTA sequence alignments Molecular Ecology Ressources 10 (1): 162-166 [link]
You are done. Apart from some other files the zip archive contains a file named index.html. Simply open this decompressed file in your modern webbrowser in order to launch the program.
In order to run SeqPHASE from commandline, you can either use these old perl scripts seqphase1.pl / seqphase2.pl or the newer python 3 scripts seqphase1.py / seqphase2.py. The zip files also contains these python/perl files.