Can deleted phone contacts visible in WhatsApp able to post chat messages? I have deleted a contact from my Android phone address book, but I still see the deleted contact in WhatsApp due to some old chats. Will the deleted contact be able to send me chat messages on WhatsApp?
Whatsapp has no relation with deleting a contact from your phone. WhatsApp uses your phone book contacts only to find who are on whatsapp, and then it shows their names in its contact tab. That's it. There is no more relation.

This means the person is still able to send you messages. His name may not be shown in the chat, but his number will be shown. This is similar to the fact that, we do receive messages in whatsapp from people who are not in our contacts, and also similar to receiving phone calls or SMS from persons whom we don't know. In whatsapp, only their number is shown in the chat screen, along with profile information, if any.

Only way to stop getting messages is to block the person. Blocking does not show on the phone of the contact you've blocked. Once blocked, the person will see that the messages he is sending, are being sent from his phone, but are not being delivered to your phone, that is, there will be no double tick, only a single tick. You'll not receive any message any calls through whatsapp from him.