В общем проблема решилась, благодаря обращению на англоязычный саппорт Yealink.
Добавили в конфиг параметр
account.X.cp_source = 1.
Публикую ответ эксперта с саппорта.
RE: Yealink SIP-T31, 46U, 48U do not display the number of the called subscr
The real source of the issue is the PBX, it response to the call with a new caller ID (your own).
See here how some folks solved it on their PBX (FreePBX)
forum.yealink.com/forum/showthread.php?tid=873&pid... but the same idea would apply to any PBX (you just need to ask that PBX people where exactly you can set it.)
The workaround would be in the Yealink phone to disable this feature of updating the Caller ID based on the SIP headers by setting (only available in provisioning):
Code:
account.X.cp_source = 1
See that thread and this Yealink guide
https://support.yealink.com/en/portal/docDetail?do...