ITU-T telephone code: and docker

I’m building Asterisk in docker and gets this question, which I’m supposed to enter via the keyboard.

ITU-T telephone code:

How do I enter this when keyboard is not possible?

Asterisk version:
git clone -b 15 --depth 1

The error seems to come from some external dependency to a package in install_prereq

sh contrib/scripts/install_prereq install
Setting up libvpb1 (4.2.59-2) ...
debconf: unable to initialize frontend: Dialog
debconf: (TERM is not set, so the dialog frontend is not usable.)
debconf: falling back to frontend: Readline
Configuring libvpb1

This is the numeric code for the region your phone system will be operating in 
(eg. 61 for Australia or 33 for France).  It is used to configure the default 
regional standards that Voicetronix telephony hardware should comply with.

ITU-T telephone code:

DEBIAN_FRONTEND=noninteractive solved the problem.