Do you want to modify Contact information for "User Mailbox" or "Mail Contact"?
All in all, you need to prepare a source file which contain the information about "the target object", "Value for Office", "Value for phone". Such as:
If you want to modify information for mail Contact, you can use command below:
Import-Csv c:/temp/source.csv | %{Set-Contact -Identity $_.Name -MobilePhone $_.phone -Office $_.Office}
If you want to modify information for contact information for user mailbox, you can use command below:
Import-Csv c:/temp/source.csv | %{Set-User -Identity $_.Name -MobilePhone $_.phone -Office $_.Office}
You can also add other attributes to above command if you want to change it. Before that, use "Get-Contact" and "Get-User" command to check whether that attribute exist for above command.
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