In phonenumberutil.h it is stated:

  // INTERNATIONAL and NATIONAL formats are consistent with the definition
  // in ITU-T Recommendation E.123. However we follow local conventions such as
  // using '-' instead of whitespace as separators. For example, the number of
  // the Google Switzerland office will be written as "+41 44 668 1800" in
  // INTERNATIONAL format, and as "044 668 1800" in NATIONAL format. E164
  // format is as per INTERNATIONAL format but with no formatting applied e.g.
  // "+41446681800". RFC3966 is as per INTERNATIONAL format, but with all spaces
  // and other separating symbols replaced with a hyphen, and with any phone
  // number extension appended with ";ext=". It also will have a prefix of
  // "tel:" added, e.g. "tel:+41-44-668-1800".

PR 2021 sought to clarify that.

For businesses that use telephony apps that span borders, displaying a list of Phone Numbers using the International and National formats in libphonenumber is inconsistent.

Actual

+1 212-500-4000
+41 44 668 1800

EXPECTED

+1 212 500 4000
+41 44 668 1800

I'd like to request a new PhoneNumberFormat of E123 that EXACTLY follows the ITU-T Recommendation E.123 formatting using only spaces.

Alternatively, add an option to allow one to disable the "local conventions" such that an INTERNATIONAL formatted number follows E.123 Recommendations.

There is value in providing local conventions, however, there is also value in providing access to standards for consistency.

Use cases:

Apps that provide Lists of Phone Numbers mixed between NANPA and non-NANPA countries (there are more of the latter than the former)
Contact Cards for Business Travellers who have multiple numbers
Anywhere consistency is a good and consistent User Interface