Hi All, I need a help with the following trigger.
I have the below trigger to update Case's adrress fields with the account's address fields as soon as a new Case is created.
I have to add the following requirement as well to it and do not know how to do it. Can some one help me? 
What need to be added: On Account object - Sales agent will collect 3 phone numbers - Home Phone, Work Phone & Mobile Phone - and we have another picklist field as "Best Number to Call" - with picklist values - Home, Work, Mobile.
If Agent select - Home - for "Best Number to Call" , Home Phone need to be carried over to Case Phone.
If Agent Selects - Work - for "Best Number to Call" , Work Phone need to be carried over to Case Phone.
If Agent select - Mobile - for "Best Number to Call" , Mobile Phone need to be carried over to Case Phone.
Case has only one Phone field. This is the tricky part for this trigger and I need help on this.
Thank you!

    public static void updateCasesWithAccountData(List<Case> newCases){
        Set<Id> accIds = new Set<Id>();
        List<Case> lstCases = new List<Case>();
        for(Case objCase : newCases){
            accIds.add(objCase.AccountId);
        }
        Map<Id, User> MapUserIDToUser =  new Map<Id, User>([Select Id, Profile.Name from User]);
        Map<ID, Account> MapAccIdtoAccount = new Map<ID, Account>([Select Id, Street__c, City__c, State__c, Zip__c from Account where Id IN:accIds]);
        for(Case objCase : newCases){
            if(MapUserIDToUser.get(objCase.ownerId).Profile.Name == 'Oncor Sales Agent' && MapAccIdtoAccount.containsKey(objCase.AccountId)){
                Case oCase = new Case(Id = objCase.Id);
                    oCase.Address_Line1__c = MapAccIdtoAccount.get(objCase.AccountId).Street__c ;
                    oCase.City__c = MapAccIdtoAccount.get(objCase.AccountId).City__c ;
                    oCase.Zip__c = MapAccIdtoAccount.get(objCase.AccountId).Zip__c ;
                lstCases.add(oCase);
            }
        }
        if(lstCases.size()>0){
            update lstCases;
        }