Unable to get results php mysqli select with bind - php

Question

I am attempting to return a result set from mysql in php using mysqli. I have attempted several different ways, but they either end in errors, or empty arrays being returned. I know the query is good because I can run it in my db admin client replacing the question mark with the string needed and it returns as expected. Does anyone see something I have missed? Looks like it should be working to me, but obviously something has to be wrong. ¯_(ツ)_/¯
<?php
class db extends mysqli{
function __construct(){
parent::__construct(PUBP_HOST, PUBP_USER, PUBP_PASS, PUBP_DB);
}
/*
--------------------------------------------------------------------------*/
function read_agency_phones($agency_in){
$returnArray = array();
if($stmt = $this->prepare("SELECT firstname, lastname, agency, phonenumber FROM employees WHERE agency = ?")){
try{
$stmt->bind_param('s', $agency_in);
$stmt->execute();
$stmt->bind_result($first, $last, $agency, $phone);
while($stmt->fetch()){
$returnArray[] = array(
'first_name' => $first,
'last_name' => $last,
'agency' => $agency,
'phonenumber' => $phone
);
}
$stmt->free_result();
$stmt->close();
return $returnArray;
} catch (Exception $ex) {
return $ex->getMessage();
}
}
return 'failed001';
}
}
$db = new db();
$results = $db->read_agency_phones("SOME_STRING");
echo '<pre>';
echo var_export($results, true);
echo '</pre>';
die;
The agency field in the database is of type VARCHAR(10).
When running the following query in admin panel, results are returned as expected:
SELECT firstname, lastname, agency, phonenumber FROM employees WHERE agency = "THE-AGENCY"