Thanks, it worked. Flow:

1. Set Webhook to Twilio console(Voice).
2. Create a index page creating call.
3. In that index page mention from, to, and URL(Redirect it to answer_call.php).
4. In answer_call.php page create establish a voice saying press 1 or press 2 using gather attribute. Method: post, action: process_key.php
5. In process_key.php, use $_POST['Digits'] and use if else condition and dial attribute to call the agent.