The two phrases are used more or less interchangeably. Materialism, physicalism and naturalism are roughly synonymous as well:Physical world ? Don't you mean material world, which is a world of illusion.
 Materialism - the doctrine that nothing exists except matter and its movements and modifications.
 Physicalism - the doctrine that the real world consists simply of the physical world.
 Naturalism - the doctrine that scientific laws are adequate to account for all phenomena
I prefer to refer to naturalism and the physical world rather than the material world or materialism for a few reasons:
For one, the physical world comprises more than matter/energy. There is also force, form, space and time, which are all in a sense aspects of matter, but not implied by the word materialism.
Also, the word materialism has been derogated by both by the Christians and Marx (dialectical materialism).
Have you seen the Wedge Document leaked from the Discovery Institute announcing its intention to "defeat scientific materialism and its destructive moral, cultural, and political legacies" and to "reverse the stifling materialist world view and replace it with a science consonant with Christian and theistic convictions"?
These Christians also declaimed, "materialist reformers [who] advocated coercive government programs" which it referred to as "a virulent strain of utopianism."
That sounds like they are conflating philosophical naturalism with Marxism. If their purpose was to demean the word, they have succeeded. Where the Christian have shit, I generally steer clear.
Hope that helps.