"Private" , "blocked" or Hide Caller Id Number (CLID)..

A few options:

Option 1 :  On the TN, CLS CLBA can block the number from being sent.

LD 20
Req       chg
type       Handset Type (Example : 1120,1210, etc)
TN        96 0 6 3
ECHG   yes

cls         CLBA
..