For each intent, you create many training phrases.
The simplest way to train your chatbot is to make publicly available datasets. You can use these:
Another way is to use your past conversations (if we're talking about developing a chatbot for customer support). This will be the most relevant source for you, and the chatbot will be more likely to reply like live chat agents.
After collecting a data set, you can start training your chatbot. Generally, it includes creating the intents for each use case and giving examples of sentences for each intent.