How to add Client Name to custom field select option

Good Day,

Hope someone could help me with this I have created a custom field for quotes Quote to:

I have made this a select field in the custom field settings I have made the value <?php echo $quote->client_name; ?> but this did not work as when I view it in the browser it is just like that in it does not bring in the client name. I have even changed it to be {$quote.client_name} and still no luck. how can I bring the client name into the custom select field dynamically?