Reference:
https://docs.microsoft.com/en-us/microsoftteams/teams-channels-overview

See the solution in the explanation below
Explanation:
To prevent guest users from calling your company's Teams users, you need to turn off the calling capability for guests in the Teams admin center. Here are the steps to follow:
Sign in to the Teams admin center with your admin credentials.
Go to Users > Guest access.
Turn off the Make private calls setting. This will disable the peer-to-peer calling feature for guests.
Click Save to apply the changes

https://www.petri.com/azure-active-directory-external-collaboration-policy

See the solution in the explanation below
Explanation:
To create a Microsoft 365 group named TeamsAdmin that can manage Teams Phone configurations without being able to manage teams and channels, you need to use PowerShell to create the group and assign the Teams Communications Administrator role to it. Here are the steps to follow:
Install the Azure Active Directory PowerShell for Graph module by running the following cmdlet:
Install-Module -Name AzureAD
Connect to Azure Active Directory by running the following cmdlet and entering your Microsoft 365 username and password:
Connect-AzureACreate a new Microsoft 365 group named TeamsAdmin by running the following cmdlet:
New-AzureADMSGroup -DisplayName "TeamsAdmin" -Description "Group for managing Teams Phone configurations" -MailEnabled $false -MailNickName "TeamsAdmin" -SecurityEnabled $true -GroupTypes "Unified" Get the object ID of the new group by running the following cmdlet:
Get-AzureADMSGroup -Filter "DisplayName eq 'TeamsAdmin'"
Copy the object ID from the output and assign it to a variable, such as $groupID, by running the following cmdlet:
$groupID = "your-object-iInstall the Microsoft Teams PowerShell module by running the following cmdlet:
Install-Module -Name MicrosoftTeams
Connect to Microsoft Teams by running the following cmdlet and entering your Microsoft 365 username and password:
Connect-MicrosoftTeams
Get the role ID of the Teams Communications Administrator role by running the following cmdlet:
Get-CsOnlineRole -Identity "Teams Communications Administrator"
Copy the role ID from the output and assign it to a variable, such as $roleID, by running the following cmdlet:
$roleID = "your-role-id"
Assign the Teams Communications Administrator role to the TeamsAdmin group by running the following cmdlet:
New-CsOnlineRoleAssignment -SecurityGroupId $groupID -RoleDefinitionName $roleID Now, you have created a Microsoft 365 group named TeamsAdmin that can manage Teams Phone configurations without being able to manage teams and channels. You can add members to this group by using the Azure Active Directory admin center or PowerShell.