Phone Validation For USA format.

Hi 
We all know USA phone number "(999) 999-9999" . How do we restrict user from invalid entry ?

We can create validation rule.

Error Condition Formula:- NOT(REGEX(Phone__c, "^\\(\\d{3}\\)\\s?\\d{3}-\\d{4}"))

Error Message:- US phone numbers should be in this format: (999) 999-9999.

if you want to add validation in controller, below is the method

public static boolean isValid(String phone){
    
        
        String PhoneRegex =  '^\\(\\d{3}\\)\\s?\\d{3}-\\d{4}';
        
        Pattern MyPattern = Pattern.compile(PhoneRegex);
        
        // then instantiate a new Matcher object “MyMatcher”
        Matcher MyMatcher = MyPattern.matcher(phone);
        if (!MyMatcher.matches()) {
        return false;
        }else{
        return true;
        }

    }

public PageReference insertValue(){
        if(Email_PhoneValidationController.isValid(testObj.Phone__c)){
            insert testObj;
        }
        else{
            testObj.Phone__c.addError('Invalid Phone Number format ...US phone numbers should be in this format: (999) 999-9999 ');
           
        }
        return null;

    }

For the above regex "9999999999" & "999-999-9999" are invalid entry. This format "999-999-9999 "  is aleo an USA format. If you want to make it valid entry then use below regex

NOT(REGEX(Phone, "\\D*?(\\d\\D*?){10}")) .