Firstly, create a "Custom Definitions" for the parameter the conversion is based on. Go to "Configure" => "Custom Definitions" and click "Create custom dimensions".

1.1. Enter a name such as "Call_disposition" (without space).

1.2. The default scope is "Event". Do not change this value.

1.3. In the description, enter "Call disposition".

1.4. Select an event parameter such as "disposition".

Do not create this custom parameter if you have already made the same one before.

Let's set up the audience. Go to the "Configure" => "Audiences" section. And click "New audience".

2.1. Then click "Create a custom audience".

2.2. Enter a name for the new audience (for example, "Answered calls"). After that, set up the conditions:
2.2.1. Click "Events" and select call.

2.2.2. Add the "Call_disposition" parameter that you created earlier.

2.2.3. For conditions, select "matches regex" and set the value: "(PROPER|REPEATED|ANSWERED)".

2.2.4. Don't forget to specify "Audience Trigger" without spaces. For example, "Answered_Calls".

Save the audience.

The last step is to set up conversion for this audience. Go to "Configure" => "Conversions". And click "New conversion event".

Give the conversion name the same as the audience trigger — "Answered_Calls" and save.

Conversion events are automatically enabled.