Thanks for asking question! Could you please confirm if you are paid Azure subscription? As Phone number availability is currently restricted to paid Azure subscriptions that have a billing address in the United States and Communication Services resources that have a US data location.
Phone numbers cannot be acquired on trial accounts or using Azure free credits.
You may want to refer to this document link for more details: https://learn.microsoft.com/en-us/azure/communication-services/quickstarts/telephony-sms/get-phone-number?pivots=platform-azp
Let us know if further query on this or issue remains.