You have a Microsoft Teams Phone deployment. The 613 7010 5XXX phone number range is allocated to the Session Border Controller (SBC). A user named User1 is configured as shown in the following…

Set-CsOnlineUser with -TelephoneNumber '+61370105555' assigns a number from the SBC-allocated range to the user's Teams Online profile, which is required for the SBC to route inbound Direct Routing calls to this specific user. Without a TelephoneNumber set on the cloud user object, the SBC has no destination to forward the inbound call to, resulting in the error external callers receive.

Setting -EnterpriseVoiceEnabled to $null via Set-CsOnlineUser is not a valid parameter value and does not resolve the missing telephone number or the on-premises attribute conflict causing inbound call failures.

Set-CsUser -OnPremLineURI is used to configure line URIs for on-premises Skype for Business or hybrid users, and applying it to a cloud-only Teams Phone user would not fix inbound routing - it is the wrong cmdlet and scope for this deployment model.

Set-CsUser -EnterpriseVoiceEnabled $false clears the on-premises Enterprise Voice attribute, which resolves a routing conflict that arises when both on-premises and online voice configurations are active on the same user object. In a hybrid or migrated environment, a residual on-prem EnterpriseVoiceEnabled setting can override or interfere with the cloud-side Teams Phone configuration, preventing proper inbound call delivery.

Grant-CsOnlineVoiceRoutingPolicy with -PolicyName $null removes the user's voice routing policy entirely, which would break the outbound calling capability that is currently functioning correctly.