Registration phone number is not saved when asked as a required field

[ParkerLP]

I've modified my checkout settings to ask for phone number as a required field. Now, a new field called Phone Number appeared on my register screen as follows:

However, when a client creates a new account, the phone number is never saved anywhere. Is this related to the E.164 format? The phone number has to be written in any given format to be saved?

Thanks for any help.