Projects can only fail in the execution phase. If the project is in the planning phase, then if it is no more, then it's considered canceled, not failed. As for the monitoring phase and the closing phase, I can't imagine a scenario where a project fails at this point (if anything, the project can be canceled at this point).
Now there are some signs that the project will definitely fail:
- Client is not communicative: This can be very problematic, as it usually results in scope creep and, consequently, a barrage of change requests.
- Scope is poorly defined: Again, this will result in scope creep.
- You're a weak project manager: You can't say no to the client/stakeholders, you can't stand up for your team members.
- Your project funding is cut: Once your monetary resources are dried up then there is no way your project will succeed.
- Your company goes belly up: Which means that all its projects are now history.
- Low quality control and quality assurance: If quality is not managed properly, then the resulting product/service (if the project is able to make it until the end) will be a disaster, and your project would be considered a failure.
- No accountability: Someone has to be accountable for the project. If no one is then there is a problem. Usually the project sponsor is accountable for the project.
- Unresponsive project sponsor: If you keep sending emails to your sponsor and he rarely, if ever, replies, then chances are your project will fail.