First of all, I won't recommend giving Access to phpMyAdmin for your Moderators.
If you want, you can install a new phpMyAdmin in your webspace and configure it to have users and you should take enough care that your Moderators canNOT do ALL Major actions like EMPTY & DROP. Better, you can provide them EDIT-ONLY only (i.e., No Insert. No Delete ONLY Update). Though this method is also having some risks... If used in a bad way, they can edit to have NULL data in your database.
Concluding... I would say that phpMyAdmin is dangerous for your site when given access to members other than YOU.
Anyhow.. All the best..