telephoneNumber attribute fails

I'm trying to use the add function:

$ldap->add($new_dn,
                attr=>['objectclass' => ['top','person',
                                         'organizationalPerson',
                                         'inetOrgPerson', 						 
'telephonenumber' => "$phone",
                                .... #OTHER ATTRIBUTES
                                    ]
                             );
The telephoneNumber attribute fails with an invalid syntax error. All 
phone numbers are entered like this: (XXX)XXX-XXXX
I've searched the list archives and can't find anyone with a similar 
problem. I believe there is a syntax problem, but a manual add using 
ldapadd works fine with the exact same data. Help!