Run Get-ADuser with filter criteria to only get those fax numbers. Pope the results to Group-Object. Make sure you specify to retrieve the fax property and group on that.
But there is always many ways to do what you want to do in powershell. Best Rule is to Filter before the Pipe with ADUser as this will save a lot of time depending on enviroment size.
$Fax_033033 = Get-ADUser -Filter {facsimileTelephoneNumber -like '033033'} -Properties facsimileTelephoneNumber | Select-Object Name,facsimileTelephoneNumber | Export-csv -notypeinformaiton c:\temp\Fax_033033.csv
$Fax_033000 = Get-ADUser -Filter {facsimileTelephoneNumber -like '033000'} -Properties facsimileTelephoneNumber | Select-Object Name,facsimileTelephoneNumber | Export-csv -notypeinformaiton c:\temp\Fax_033000.csv
Here's another little tip always check to see what Covertto-CSV will show up.
PS C:\WINDOWS\system32> Get-ADUser -Filter {facsimileTelephoneNumber -like '033033'} -Properties facsimileTelephoneNumber | Select-Object Name,facsimileTelephoneNumber | ConvertTo-Csv
#TYPE Selected.Microsoft.ActiveDirectory.Management.ADUser
"Name","facsimileTelephoneNumber"
"Lastname, FirstName","(123) 456-7890"
The Attribute for Fax shows in Aduc as FacsimileTelephone Number
Try this approach. You want to loop through the number, query AD and then you can use calculated expressions to get the count for every number. Each result is stored in your results variable and then you can export it to a CSV if you so desire. Double check the LIKE statement, there were no wildcard characters, so I added them.