How to send value present in the custom field using trigger

Hi Nikesh Spakota

If you're looking to update the native phone number field on the requester (user rather than ticket), then you would need a webhook to update the user specifically, on the below post by Sam there is a good description of how to achieve this - specifically the section "Create a trigger that writes the phone number on ticket creation":
https://support.zendesk.com/hc/en-us/community/posts/4552066628890/comments/4552733850266

There are some very useful notes in the comments section as well. Hope this helps you out!

Hi Nikesh,

From: Can I add custom ticket field values to email notifications? – Zendesk help

Answer

Yes, add placeholders referencing the custom ticket field to the subject or body of your trigger or automation.

1. Open Admin Center, and navigate to Objects and rules > Tickets > Fields. Locate your custom ticket field, and copy the Field ID number.

2. Go to the trigger or automation sending the e-mail notification and add the placeholder there. You need to use the following format: {{ticket.ticket_field_<field ID number>}} 

Example:

For the custom field ID number: 900001783063 you will use this placeholder: {{ticket.ticket_field_900001783063}}

The value of the custom ticket field in the ticket will be added to the email notification sent by your trigger or automation.

For more information, see the article: Using placeholders.