On further research I have found the FCC is aware of the issue of
spoofed caller IDs. The practice is illegal and at least two miscreants have been caught and fines totaling $183 million have been levied in 2017, but the difficulty in tracing these calls to their source (which is often outside U.S. jurisdiction) means only a tiny number actually get caught and an even smaller number are prosecuted. This latest tactic of using the target's phone number or some portion thereof) appears to be intended to counter the FCCs tracking efforts as the spoofed numbers are used only once.
I have not been hit with spam texts — yet, but a recent update to
NoMoRobo includes an experimental feature that attempts to block or at least segregate spam
text messages! This is based on "whitelisting" your Contacts list and NoMoRobo's list of known spam sources. Once suspect texts have been segregated the user has the option to block or whitelist the sender.
Surely better tools will emerge, but in the meantime spoofed caller ID's can be reported to the FCC
here.
