Why is there no relationship between pressure and temperature in solids and liquids?

Answer

For a gas, there is a relationship between pressure and temperature if you keep the volume constant.

In a sense, this is also the case for a solid and a liquid: if you keep the volume constant and you increase the temperature, you will have to exert a force to compensate for the thermal expansion. A tension (force per unit area) is created in the material that depends on its coefficient of thermal expansion and its modulus of elasticity.