Se você realmente gosta de one-liners:
Get-ADGroup -Filter {displayName -eq 'groupName'} | Get-ADGroupMember |Foreach-Object {Get-ADUser -Identity $($_.SID) -Properties name,sn,givenName,otherTelephone} | Format-Table name,sn,givenName,otherTelephone
Se você quiser manipular os objetos User ainda mais, talvez queira armazená-los em uma matriz:
$Group = Get-ADGroup -Filter {displayName -eq 'groupName'}
$Members = Get-ADGroupMember -Identity $Group
$Users = @()
Foreach-Object -InputObject $Members -Process {$Users += (Get-ADUser -Identity $_.SID -Properties *)}
$Users | Format-Table name,sn,givenName,otherTelephone