You can't call it anonymous or no country restriction and ask for a phone number before giving someone an account.
It should default a new visitor to a new account they can choose to keep by entering their email address.
Nitrogen Sports has done this with bitcoin sports betting for years and its great for letting people see the site easily and allows you to keep an account if you're gambling a lot.
honestly I'm not even sure what the phone number is used for cause I registered and put my phone number , made a deposit and a withdrawal and nothing was sent to my phone
so I don't really see a use for it , maybe you can just use a fake phone number but not sure if you may need that phone number in the future for withdrawals or verification
Can the OP answer why they need phone number as it seems there's really no use of it? Is it really important to require phone number from your potential players?