To build a working phone app, your app needs to use Upsales API and the phoneCall endpoint.
Get a list of phone calls by querying for phoneCall objects
GET https://integration.upsales.com/api/v2/phoneCall
Get a single phoneCall object
GET https://integration.upsales.com/api/v2/phoneCall/:id
Update a phoneCall object
PUT https://integration.upsales.com/api/v2/phoneCall/:id
Add a phone call into Upsasls
POST https://integration.upsales.com/api/v2/phoneCall
For more info about Upsales API, click to go to the documentation