Your main problem is slowness, but at the same time it makes you incredibly strong. If there are any unforeseen circumstances, problems or force majeure, you are able to analyze the situation absolutely calmly and make an informed decision that will be the only right one at the moment.
And it is true that you are tense for a long time, but you do it in a charming and qualitative way.
However, if you have done something before or have experience, then you will quickly perform this kind of task exactly as the situation requires.
Besides slowness, there can be another disadvantage for many: When a phlegmatic is asked to do something, he will do exactly what is required of him, and beyond or beyond that he will not exert himself. Therefore, it is necessary to overestimate the demands on themselves.