Fix phone number constraints.

src/main/java/seedu/address/model/person/Phone.java

@@ -11,7 +11,8 @@ public class Phone {
 
 
     public static final String MESSAGE_CONSTRAINTS =
-            "Phone numbers should only contain numbers, and it should be at least 3 digits long";
+            "Phone number should only contain numbers. Phone number should be at least 3 digits long "
+                    + "and should not be longer than 8 digits.";
     public static final String VALIDATION_REGEX = "\\d{3,}";
     public final String value;
 
@@ -30,9 +31,11 @@ public Phone(String phone) {
      * Returns true if a given string is a valid phone number.
      */
     public static boolean isValidPhone(String test) {
-        return test.matches(VALIDATION_REGEX);
+        return test.matches(VALIDATION_REGEX) && (test.length() >= 3 && test.length() <= 8);
     }
 
+
+
     @Override
     public String toString() {
         return value;