I have 4 phone fields, I need the preferred phone field to be a required field when more than 1 phone number is entered. 
Preferred phone number - should be entered ONLY when 2 or more phone numbers are entered. Any help is appreciated. TIA

 I have 4 phone fields, I need the preferred phone field to be a required field when more than 1 phone number is entered. 
Preferred phone number - should be entered ONLY when 2 or more phone numbers are entered. Any help is appreciated. TIA

The rule should fire if at least one phone field is populated and it requires the user to select a Preferred Phone. It works on Contacts, but won't fire when a phone field is populated on Leads. I'd like to figure out why and find out what the correct formula is. Thanks.

AND(
OR(
ISNEW(),
ISCHANGED(tcf_Phone_Home__c),
ISCHANGED(MobilePhone),
ISCHANGED(tcf_Phone_Work__c)
),
NOT(ISBLANK(tcf_Phone_Home__c)),
NOT(ISBLANK(MobilePhone)),
NOT(ISBLANK(tcf_Phone_Work__c)),
NOT(ISCHANGED(npe01__Preferred_Phone__c)),
OR(
ISCHANGED(npe01__Preferred_Phone__c),
ISBLANK(TEXT(npe01__Preferred_Phone__c))
)
)