Completely new at powershell... can I get a little assistance with AD?

Hello, I have a challenge that I believe powershell is probably perfect for, but I have no idea how to do it.

I need to populate the "IP Phone" field in Active Directory user accounts for each of my users that have an IP phone. Currently, the IP Phone attribute is blank. Fortunately, Cisco creates a hidden value for each mailbox we created.

The attribute is called "ciscoEcsbuDtmfId". The value is a 4 digit number (the extension). I am looking for a way to copy or clone the value from "ciscoEcsbuDtmfId" to "ipPhone" for each user, so I don't have to manually enter them all in.

Can anyone offer some assistance?

Thanks!
Max