Hi,
You need to follow the disciplinary process. Try to reach the employee through alternate options like: 1) through email, 2) alternate emergency contact number if taken at the time of joining.
In case of no response, serve a warning letter through Registered Post with Acknowledgement Due (RPAD). The warning letter should be dispatched to both the personal and permanent address as available in the personal file.
Provide a sufficient time frame for the employee to report back. Wait for the RPAD Acknowledgement due. Check whether it is signed by the employee or others.
Proceed with the termination process if the employee fails to report back even with the sufficient time frame provided.
Keep a copy of all communications in the personal file of the employee.