LDAP Phonebook Settings for iOS Devices
Preferences > Accounts > Add "Other" Account
Then choose “Add LDAP Account”
Probably you want a useful description otherwise iOS will use the servername.
Now you should save the settings.
Using the phonebook
Go to your phonebook and tap on the phonebook name you configured before.
Now you can search for a name
Since the iPhone only searches for prefixes by default you can use a * in the search field.