You can do whatever you want by hand of course but this stuff gets hairy quickly and I would strongly recommend taking the learning curve hit up front for DBIx::Class or something similar. If you want a bit more more raw try SQL::Abstract.

use SQL::Abstract;

my $sql = SQL::Abstract->new;

my %data = ( name => 'test_name',
             phone => 'test_phone',
             city => 'test_city',
             country => 'test_country' );

my ( $statement, @bind ) = $sql->update("phone", \%data);

printf("SQL --> %s\n        %s\n\n",
       $statement, join(",", @bind) );

delete @data{qw( phone city )};

( $statement, @bind ) = $sql->update("phone", \%data);

printf("SQL --> %s\n        %s\n\n",
       $statement, join(",", @bind) );

__END__
SQL --> UPDATE phone SET city = ?, country = ?, name = ?, phone = ?
        test_city,test_country,test_name,test_phone

SQL --> UPDATE phone SET country = ?, name = ?
        test_country,test_name
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