You can use Jay Sheth's sample code then get latitude and longitude:
$json = file_get_contents('http://open.mapquestapi.com/geocoding/v1/address?key={your_key_here}&location=Lancaster,PA');
$jsonArr = json_decode($json);
$lat1 = $jsonArr->results[0]->locations[0]->latLng->lat;
$lon1 = $jsonArr->results[0]->locations[0]->latLng->lng;