Change apple id from mobile number to email

If you already have an Apple ID that's an email address, you might not be able to change it to a mobile phone number. However, you can associate your account with different phone numbers or email addresses on your 

Apple ID account page.

To change Apple ID from Phone number to email ID see the 3-step process below, vice-versa is not possible.

1. Create an Apple ID using an email ID. --> How to create a new Apple ID
2. Sign out from your Apple ID on your device which is a Phone Number now. --> Sign out of iCloud on your iPhone, iPad, iPod touch, Apple TV ...
3. Sign in using the newly created Apple ID. --> Sign in with your Apple ID - Apple Support (IN)