The phase of matter that maintains its shape when force is applied to it is a solid.

Here's why:

* Solids have a fixed shape and volume because their particles are closely packed together and held in a rigid structure by strong intermolecular forces. This makes them resistant to changes in shape.

Let's compare this to other phases:

* Liquids take the shape of their container but maintain a fixed volume. They have weaker intermolecular forces than solids, allowing their particles to move more freely.

* Gases take the shape and volume of their container. They have very weak intermolecular forces, allowing their particles to move freely and spread out.

So, while a liquid might change shape slightly when pressure is applied, a solid will resist that change and maintain its original form.