$\Phi$ is the union of all triangles that are symmetric of the triangle $ABC$ wrt a point $O$, as point $O$ moves along the triangle's sides. If the  area of the triangle is $E$, find the area of $\Phi$.
1. To understand the problem, we need to clarify what it means for a triangle to be symmetric with respect to a point. If a point \( O \) lies on a side of triangle \( ABC \), the symmetric triangle with respect to \( O \) is the reflection of \( ABC \) across the line containing \( O \).

2. Consider the triangle \( ABC \) with vertices \( A \), \( B \), and \( C \). Let \( O \) be a point on side \( BC \). Reflecting triangle \( ABC \) across \( BC \) will produce a new triangle \( A'B'C' \) such that \( A' \) is the reflection of \( A \) across \( BC \), and \( B \) and \( C \) remain unchanged.

3. Similarly, if \( O \) lies on side \( CA \), reflecting triangle \( ABC \) across \( CA \) will produce another triangle \( A''B''C'' \) such that \( B'' \) is the reflection of \( B \) across \( CA \), and \( A \) and \( C \) remain unchanged.

4. Finally, if \( O \) lies on side \( AB \), reflecting triangle \( ABC \) across \( AB \) will produce another triangle \( A'''B'''C''' \) such that \( C''' \) is the reflection of \( C \) across \( AB \), and \( A \) and \( B \) remain unchanged.

5. The union of all these reflected triangles as \( O \) moves along the sides of \( ABC \) will cover a larger area. To find this area, we need to consider the geometric properties of the reflections.

6. Each reflection of \( ABC \) across a side of the triangle will produce a triangle with the same area \( E \) as \( ABC \). Since there are three sides, and each side can be reflected to produce a symmetric triangle, the total area covered by these reflections will be three times the area of \( ABC \).

7. However, we must account for the fact that the original triangle \( ABC \) is included in the union of these reflections. Therefore, the total area of \( \Phi \) is given by the sum of the areas of the three reflected triangles minus the area of the original triangle \( ABC \).

\[
\text{Total area of } \Phi = 3E - E = 2E
\]

Conclusion:
\[
\boxed{2E}
\]