More than 90% of a project manager's job is done in the Planning and Execution phases. Planning is where you create the roadmap you are going to follow to the end of the project, and Execution is where you make it happen. Which is more important? Neither and both. If you are not a very good planner, then problems will occur in the Execution phase because you probably will be "winging" it at some point, which is not very good project management. At the same time, you can save projects during execution even if the first planning was less than excellent.
Although the project manager must be able to do "workarounds" for unexpected problems, if you have planned well, there will be few of these. You will not, repeat not, have a project that goes exactly as planned from day one to the end of the project. That happens only in theory. If you are using people on your project (or I guess animals too), something will happen that is unexpected. But plan for the best.
There are also cases where projects aren't planned completely, but a good project manager manages to bring the project in close to time and cost. This is not recommended procedure, but all of us have had to do it. Sometimes the organization is ready to start at a certain date and does not build in the necessary planning time. My only hope is that they are fortunate enough to have a professional project manager in place and that he or she can draw on enough intelligence and experience to bring it off.
So, having a project manager who can handle workarounds or any type of unexpected action taking place, and who understands the various organizational structures in which he/she finds him/herself, means that the Execution phase of the project is one where the actual project