https://www.reddit.com/r/PowerShell/comments/8ayhm5/ad_getadobject_from_gc_setaduser_on_domains/

Update-PhoneNumber.ps1

#requires -Module ActiveDirectory
[CmdletBinding(SupportsShouldProcess)]Param()

$PSDefaultParameterValues = @{'*:ErrorAction'='STOP'}

$dcHash = @{}
try {
    Get-ADForest | Select-Object -ExpandProperty Domains | ForEach-Object {
        $domain = $psitem
        $dc = Get-ADDomainController -Discover -DomainName $domain | Select-Object -ExpandProperty hostname
        $dcHash.Add($domain,$dc)
    }
}
catch {
    Write-Error -Message ('Failed to load domain hash: {0}' -f $psitem.exception.message)
}

try {
    foreach ($key in $dcHash.Keys) {
        Get-ADUser -Filter {officePhone -like "*"} -Server $dcHash[$key] -Properties name,officePhone | ForEach-Object {
            if ($PSCmdlet.ShouldProcess( ('[{0}] User: {1} Phone: {2}' -f $key,$psitem.sAMAccountName,$psitem.officePhone) ) ) {
                $psitem | Set-ADUser -OfficePhone "SomeString" -Server $dcHash[$key]
            }
        }
    }
}
catch {
    Write-Error -Message ('Failed to update: {0}' -f $psitem.exception.message)
}