So you want to answer incoming regular phone calls on the phone device?
This seems to be possible on newer Android versions, but not on older ones,
It would require you create your own custom Android app, and would require a fair bit of development.
Another solution is to use Twilio for a virtual phone number, and use Twilio speech support and Bot Libre's Twilio integration.
If you would like us to develop a solution for you contact [email protected]