How to enable MFA Phone (voice call) per user?

Question

i have a few users that are unable to add their numbers to their accounts.

https://myaccount.microsoft.com/?ref=MeControl

under their Authentication methods policy its set to disabled. Not sure why only these few users have it as disabled. Not sure where to look.

Migration status is in progress.

For the particular use I see Authentication method Disabled by policy - again this is only happen for a small group of users.

thanks