Update index.md

Added a note on that when phone is set in trait, Iterable will perform some checks on the phone number.

Added the following note into ## Identify section:
"If you send phone in traits, Iterable will perform some checks on the phone number before showing in User Profiles. You can read more about Iterable's phone number field here: https://support.iterable.com/hc/en-us/articles/211970843-SMS-Overview-#contact-phone-numbers."

Author: tanjinhong72

src/connections/destinations/catalog/iterable/index.md

@@ -24,6 +24,8 @@ When you call `identify` with one of Segment's sources, Segment calls Iterable's
 
 Iterable keys users by `email` or a user ID. This user ID will be the Segment `userId` if sent. To use a Segment `userId` for identify calls, first call identify with both a `userId` and `email`. Iterable won't accept the request and throws an error if you fail to send one of either the `userId` or `email`.
 
+If you send phone in traits, Iterable will perform some checks on the phone number before showing in User Profiles. You can read more about Iterable's phone number field here: https://support.iterable.com/hc/en-us/articles/211970843-SMS-Overview-#contact-phone-numbers.
+
 <!-- commented out because this functionality isn't currently working ZD#355518
 ### Merge Nested Objects