The .conf file format has changed quite a bit since then,
<?xml version="1.0" encoding="UTF-8"?>
<config>
<sourcemap>
<maps datatype="bibtex" level="user">
<map map_overwrite="1">
<map_step map_field_source="journal" map_match="Physical\sReview" map_replace="Phys. Rev."/>
</map>
</maps>
</sourcemap>
</config>
should do the right thing now.
The Biber documentation is a good place to start your research. Have a look at §3.1.2. The sourcemap option, pp. 13-20, esp. p. 17 where we have the example
<map map_overwrite="0">
<map_step map_field_source="AUTHOR" />
<map_step map_field_set="SORTNAME" map_origfieldval="1" map_final="1"/>
<map_step map_field_source="SORTNAME" map_match="\A(.+?)\s+and. ∗ " map_replace="$1"/>
</map>
Of course you can also have a \DeclareSourcemap in your .tex document
\DeclareSourcemap{
\maps{
\map{
\step[fieldsource=journal,
match=\regexp{Physical\sReview},
replace=\regexp{Phys. Rev.}]
}
}
}
which does the same, but is easier to keep track of, I find. It is easy to forget about a biber.conf and be confused about the output, with the sourcemapping done in the .tex file at least one is more likely to see the relevant code.