Hi Avivey, many thanks for the feedback.

Issue 1: Thanks for clarifying that, however when I then browse to the http://phabricator.domainB.local I get the error: "[Core Exception/Exception] Specified domain phabricator.domainB.local is not configured for Phabricator requests. Please use http://phabricator.domainA.local/ to visit this instance." I've rebooted the server, stopped/started the phabricator daemons but it's still only responding to http://phabricator.domainA.local .

Issue 2: I followed your example but I'm still getting the same error:
root@phabricator:~/phabricator-install/phabricator# ./bin/config set phabricator.allowed-uris ["http://phabricator.domainA.local"]
Usage Exception: Config key 'phabricator.allowed-uris' is of type 'list<string>'. Specify it in JSON.

The shell is probably eating away the ". Try surrounding the whole argument with ' to stop it.

What does ./bin/config get phabricator.base-uri say?

Base URI is correctly set in the local configuration though it is still not recognised as being configured for Phabricator requests, only DomainA is.

phabadmin@phabricator:~/phabricator-install/phabricator# ./bin/config get phabricator.base-uri
{

"config" : [
  {
    "key"    : "phabricator.base-uri",
    "source" : "local",
    "value"  : "http:\/\/phabricator.domainB.local"
  }
]

}

Allowed URIS; This didn't return an error this time (the web UI is still showing no entries (Current Value: {}) but get phabricator.allowed-uris is showing the new entry (should the value contain the square brackets?)

./bin/config set phabricator.allowed-uris '["http://phabricator.domainA.local"]'

phabadmin@phabricator:~/phabricator-install/phabricator# ./bin/config get phabricator.allowed-uris
{

"config" : [
  {
    "key"    : "phabricator.allowed-uris",
    "source" : "local",
    "value"  : [
      "http:\/\/phabricator.domainA.local"
    ]
  }
]

}

I found this link: https://secure.phabricator.com/book/phabricator/article/advanced_configuration/

//Phabricator supports the following configuration sources, from highest priority to lowest priority:

Database: Values are stored in the database and edited from the web UI by administrators. They have the highest priority and override other settings.
Local: Values are stored in conf/local/config.json and edited by running bin/config.//

If the Web UI is blank but I've made the changes to the local config does this mean the local config won't be applied?

When you load the configuration web page, the effective configuration is highlighted yellow. If the database value is not null, it might be overriding it, but ./bin/config get should show all the configured values.

The Web UI, in the Config > Core > phabricator.base-uri section it has the following:

SOURCE VALUE
database (empty)
Local http://phabricator.domainA.local

From the command line it say the base URI has been updated correctly (is this part of the entry correct? http:\/\/ rather than just http:// ?)

phab_admin@phabricator:~/phabricator-install/phabricator# ./bin/config get phabricator.base-uri
{

"config" : [
  {
    "key"    : "phabricator.base-uri",
    "source" : "local",
    "value"  : "http:\/\/phabricator.domainB.com"
  }
]

}

I've rebooted, stopped and restarted the phabricator services (./bin/phd stop and ./bin/phb/start), so no idea why the web UI is not updating??