The PHP built-in functions for accessing mysql are IMO just too messy and unportable (to other databases) to be really useful, though it does have a nicer layer called DB on PEAR.

Anyway, using perl's DBI or PHP's DB should not make much difference in practice. Unless ofcourse you already know perl, in which case you should probably be using perl :-). DBI is one of the most tested and used CPAN libraries out there (especially in conjunction with its MySQL adapter DBD::mysql) so you don't need to worry about that.

If you are interested in a higher level abstraction and you'd like an object-oriented interface, you can take a look at Class::DBI which is build on top of DBI and can be very useful. I'm sure PHP has something similar, but I haven't looked for it. Bottom line: if you know perl well enough, there is no reason to turn to PHP just for database support.