The usage group of that API (I assumed you are talking about this API) is Heavy which means the rate limit is 10 times per 60 secs. So calling the API every 5 secs will hit the rate limit for sure. And will be the same limit on the production environment.
However, for such use case, you should not poll but use one of the notification filters to get notified when there is an incoming call, the call is answered or not then the call is disconnected.
If you don't need lots of data, you can use the presence event notification with the filter "/presence?detailedTelephonyState=true"
If you need lot more data and different call statuses, use the telephony session even notification filter.
Read this blog and this blog for further information about telephony session event notifications and some use cases.
