I didn't understand if you are using the WebRTC Phone from Genesys Cloud Desktop or if you have created/integrated your own WebRTC phone into your Angular app.
If the question is about using the WebRTC Phone from Genesys Cloud Desktop and invoking a request to answer the call from a separate application (Angular or else), you can have a look at the following blog - Clarifying call control support to answer a call or to make a call using Platform API .
It covers different type of phones and setup - and describes constraints and limitations - you should find yours in it.
Thanks a lot @Jerome.Saint-Marc . going through the article helped me resolve the issue.
Just FYI, I integrated the WebRTC phone in my Angular app and was not receiving the call earlier, now its connecting successfully.