Depending on the lifecycle methodology in use for the project, they could be
initiation, planning, execution, control and close (Waterfall etc.), or concept,
inception, elaboration, construction and transition (RUP), or project
preparation, blueprint, realization, final preparation and go live and support
(SAP ASAP) etc.

In my opinion, the most important phase of a project is the “current” phase
of the project – whichever phase the project is currently in. Here is the reason
why.

First, I will take the example of one random phase – say inception, or
planning – where we plan the entire project. If the project is not planned
right, core requirements identified, project teams assembled, or funds secured,
or next phase not planned properly or any of the other tasks not executed right,
the entire project could fail. Therefore, at this time of project execution,
this phase is the most important phase.

Now, let’s move on to the next phase of the project. While elaboration or
execution or realization efforts are going on, if those efforts and task
included in those phase are not executed correctly, or next phase is not planned
correctly, no amount of success in the previous phase would matter. The project
would still fail.

Same is the case with construction, or transition or go live. If we don’t
construct the product right, or verify that the constructed product meets the
demand (requirements) or we don’t ensure the go live and support are successful,
the project is still termed as a failure.

Therefore, every phase is a building block and is just as critical for the
overall success of the project. Once a project starts, the project manager
cannot rest assured with one successful phase, that the entire project would be
a success. Once “every” phase of the project is successfully executed, once the
project is closed successfully, then the project is “successfully delivered”.
Therefore, the most important thing for a project manger to do is to concentrate
on the current phase, reevaluate previous phase’s planning efforts, and plan for
the next phase, handling current issues and mitigating future risks.