possible to only recieve calls from contacts?

I can think of two options:

The first is Family Allowances that allows you to provide numbers that he can call and receive calls from.  This is like $5/mo, I believe.  I don't know if there's a limit as to how many you contacts you can add, and this has to be maintained every time a new contact needs to be added.

The second is to look at the phone's user manual and see if it can block unknown callers (in the fashion you speak).  It will send them to voicemail.  This means any doctor appointment reminder calls and that not programmed in his phone would get sent as well.  Some have a full-on block.  I don't know how he handles his voicemail currently.  (a lot of those spam calls say "call us back at this number", and if he calls them back, you're back to him answering the phone)

T-Mobile doesn't have a copy of your phonebook, so they can't link directly to "only folks I have in the phone book".  I THINK these are your two options.