Using placeholders, getting unexpected SQL errors

[ok]

This is a simple SQL insert...

$insert_cmd = "INSERT INTO PhoneNumbers 
                 (cusID, adtID, pntID, phnPart1,       
                  phnPart2, phnPart3, phnExt)
               VALUES 
                  (?, ?, ?, ?, ?, ?, ?)";

$phone_insert = $gcssDBH->prepare($insert_cmd);

...

$phone_insert->execute(
                        $row->{'cust_id'}, 
                        $adtID, 
                        $phoneNumberTypes->{'Day'},
                        $row->{'cust_phac'}, 
                        $row->{'cust_phpx'}, 
                        $row->{'cust_phsx'}, 
                        $row->{'cust_phex'}
                      );

...but I get this error: You have an error in your SQL syntax near '89, '45')' at line 4 (line 4 of the query, that is)

...with these values assigned to the variables:

  $row->{'cust_id'}   == 3048770
  adtID               == 2
  pntID               == 3
  $row->{'cust_phac'} == 704
  $row->{'cust_phpx'} ==  53
  $row->{'cust_phsx'} == 2 89
  $row->{'cust_phex"} == 45

I don't see anything wrong with the code. Does something jump out at you? Yes, $row->{'cust_phsx'} == "2 89" but I don't see why that should make a difference. Obviously, I'm wrong. I'm under the impression that using placeholders gives me the right to avoid explicitly escaping naughty characters.