Log Phone Updates in Description Field

This trigger logs changes to an Account’s Phone field in its Description. It displays the old and new phone numbers, maintaining an audit trail.

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Solution:

trigger AccountTrigger on Account (before update) {

              if(Trigger.isUpdate){ if(Trigger.isBefore){
                     AccountTriggerHandler.updateDescription(Trigger.New, Trigger.oldMap);
                }
        }
}
  public class AccountTriggerHandler {
        public static void updateDescription(List<Account> accList,Map<Id,Account> oldMap){
                  for(Account acc:accList){
                        if(acc.Phone!=oldMap.get(acc.Id).Phone){
                            acc.Description=’Phone is updated! Old Value :
                            ‘+oldMap.get(acc.Id).Phone+’ & New Value :
                            ‘+acc.Phone;
                    }
           }
      }
}