When an agent is busy on a direct call on the mobile and an IVR call is forwarded to him/ her then, the IVR call is kept on waiting. Once the agent disconnects his/ her initial call then, the IVR call gets connected to that agent. 

Note: The system first tries to forward the IVR call to the agent who is busy on the direct call as per the ringing time (default 30 seconds). If it fails to connect to that agent, the call is forwarded to another agent.