It does not work

I made the following code:

function onChange() {
var callerId = g_form.getValue('caller_id');

if (callerId) {
// Fetch the caller's record
var caller = new GlideRecord('sys_user');
if (caller.get(callerId)) {
// Get the mobile phone from the caller's record
var mobilePhone = caller.mobile_phone;

// Set the u_call_back field in the incident form
g_form.setValue('u_call_back', mobilePhone);
}
}
}

But it doesn't work for me in SOW - service operation workspace