trigger AccountTrigger3 on Account (before update, after update) {
	if (Trigger.isUpdate) {

	    if (Trigger.isAfter) {
		    SanjayGupta03_Trigger.updateOpportunityAmount(Trigger.New, Trigger.oldMap);
	    }

	  }

}

public class SanjayGupta03_Trigger {
	public static void updateOpportunityAmount(List<Account> newList, Map<Id, Account> oldList){

		for (Account acc : newList) {
			if (acc.Phone != oldList.get(acc.Id).Phone) {
				System.debug('Value is Updated');
			}
		}
		
}