I’ve done something similar and my guess is they preformed a migration in 2009 and didn’t want to force current users to provide phone numbers so they used the

I’ve done something similar and my guess is they preformed a migration in 2009 and didn’t want to force current users to provide phone numbers so they used the default value as a placeholder/note that reminds them to special case these users who were grandfathered in under the old rules.