Applies To

Call2Teams - Customer

Note: Phone App is available as an additional 'add-on' to existing PBX or Trunk services. If the options is not available in the portal then the service has not been provisioned to the account and needs to be enabled via the licensing provider. 

Phone App is currently only avalible to Call2Teams for PBX users. (Call2Teams for Trunks coming soon!) 


This article outlines some of the common issue with setting up Phone App and the suggested resolution.

1) Users not showing in the Add Users list

Cause 1:

The most likley cause of this is a user or the tenant not being set to Teams Only mode.

In the Sync Now log the following type of message will be reported:

Excluded 2 users ineligible for Phone App as they are not in TeamsOnly mode for Teams Upgrade.

Review this setup article for remedial instructions on setting a user or the entire account to Teams Only mode: Click here

If your still getting this error message then please see this link regarding TeamsOnly Mode still not working

Cause 2:

A second reason for user not showing is because the Teams service is configured with Large Tenant Mode. In this mode, any user specified in the base Azure Groups for synchronisation will be assumed to have a Phone System licence and not eligible for Phone App.

Resolve this by using the setting for 'Azure AD Phone App Groups' and specify groups where users are members that will be using Phone App. 

  • Ensure the same group is not specified in both Large Tenant Mode AD Group sections, 
  • Ensure users do not belong to the core specified AD groups if they are going to use Phone App, they should only be a member of the group detailed in Azure AD Phone App Groups to be eligible for Phone App.

2) Calls not going through to a Teams user - '603 Call Declined' in call log

This issue is a result of the customer Microsoft 365 account not being correctly set for External Access and allowing the Phone App domain.

The solution is to allow the Phone App domain on the Microsoft 365 tenant in the external access settings, or allow all domains

Directions for setting External Access for Phone App are available in this article Phone App (Overview)

Note: it can take some time (maybe several hours) for the External Access domain settings to take effect in the Teams admin center

3) Call CANCEL does not work as expected - Pools 

In some call scenarios when the PSTN/PBX sends a CANCEL through to Phone app the Teams side of the call may continue to ring out for a few seconds with delay. This can happen if the PSTN ends a call before the Teams client accepts or if the PBX sends a Cancel to say the call was answered elsewhere.

We are actively working on the issue with Microsoft engineers who have identified the issue affects tenants which are in a "poolless" state. To identify if your tenant is affected run a Get-CsTenant command and check to see if you have a pool value similar to the below;

  • Get-CsTenant

We will be updating our guidance shortly once we have clarification from Microsoft on how to raise tickets for this issue.

4) Unable a take call off hold

Some Teams clients are affected by an issue with taking a Phone App call off hold (after the user has put the call on-hold).

This is a known issue and is being resolved with a software update.

Affected customers should log a ticket to be notified when the issue is resolved.

4) iOS - Unable to receive inbound or outbound calls 

There are currently intermittent issues with Phone App on IOS devices, whereby the user needs to clear Teams app data to access and use Phone App again – typically every 2 hours. In the event of an inbound call being made during the period where the app requires its data clearing, the call will show as a missed call once the app data is cleared. This issue doesn’t affect Teams to Teams calls in the main Teams App.

The likely cause of this is an outdated iOS version. The below graph will advise you of any outbound and inbound call issues and its corresponding iOS versions. 

iOS Version
Compatible iPhones
15.2.1 and AboveiPhone 6s and aboveWorking
15.1 and Below
No Inbound and Outbound Calls

In some instances you may also require to clear the app data on your iPhone after updating your iPhone to the latest version (15.2.1 and above). Settings > Teams > Clear App Data.

Please note the version of Microsoft Teams installed could affect the inbound and outbound calls. Install the latest version. Confirmed Version: 4.1.0 and above. 

How to Clear Cache on an iPhone: Settings > Teams > Clear App Data.

5) Using Phone App with a Trunk service (call failure)

Currently Phone App is optimised for operation with the PBX service as a softphone extension.  Compatibility with Trunk services is planned but not yet available. Attempting to user Phone App with a Trunk service will cause the call to fail with an error message.

It is planned that the Phone App will work with a Trunk service and this article will be updated accordingly.

Using Network view (F12) to see error message

In rare cases we may require you to run a network view while trying to place a call with Phone App. To do this open the network view tab within your browser (the Teams client should be running in the browser) and press the call button with a number populated. 

Clicking on the word "Dial" should then give you a response Tab to see the error code (example below)