Why is the React Native app being rejected by Android Play console?

Please make sure to ask for permission before user uses any call/sms permissions. You can use Permissions from react-native to handle that

Also, you should provide terms that when user signs-up for uses that what permissions your app requires and whether you share with third parties.

It is not easy thing and worth making some research.

Btw, was your ios get accepted?

Follow requirements for default handlers 
Given the sensitive user information that an app accesses while serving as a default handler, your app cannot become a default handler unless it meets the following Play Store listing and core functionality requirements:

Your app must be able to perform the functionality for which it's a default handler. For example, a default SMS handler must be able to send text messages.
Your app must provide a privacy policy.
Your app must make its core functionality clear in the Play Store description. For example, a default Phone handler should describe its phone-related capabilities in the description.
Your app must declare permissions that are appropriate for its use case. For more details about which permissions you can declare as a given handler, see the guidance on using SMS or call log permission groups in the Play Console Help Center.
Your app must ask to become a default handler before it requests the permissions associated with being that handler. For example, an app must request to become the default SMS handler before it requests the READ_SMS permission.

Read through this article that is specifically for your case:
https://developer.android.com/guide/topics/permissions/default-handlers