my($id, $name, $phone);
$sth->bind_columns(undef, \$id, \$name, \$phone);
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$sth->bind_columns(\my ($id, $name, $phone));
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And, for the same reasons, you should use prepare_cached instead of prepare.

Choosing prepare or prepare_cached really depends. The caching is a slight overhead, so if I can reasonably arrange my SQL so that something is only prepared once (or if its used just once anyway), then I'll just use 'prepare'. Or if you're dynamically creating a SQL statement (lets say a million times) and the number of possible unique combinations is large, then you don't want to use prepare_cached, e.g. you have a couple of 'IN' clauses, and each one might have 1-100 elements, so you end up with something like:

select stuff
from table
where field1 in (?,?,?,?)
and   field2 in (?,?,?,?,?)
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