I was referring to the chance that some pieces of Mars might be
on the Martian moons that could be studied, not send a mission
there just for that objective. The Martian debris would be a
serendipitous bonus.

And I am sure you will agree that any pieces of Mars on Phobos
will likely be far less contaminated than any Martian rocks that
landed on Earth. And as for potential fossils, that would be
another serendipitous bonus. Just as some scientists have
speculated that Earth rocks and fossils might be found on
the Moon from ancient impacts.

Could enough small debris that would survive the impact and flight
into Martian orbit be enough to form into Phobos and Deimos, rather
than the two moons benig flung into space as whole chunks?

Or how about the moons coalesed with Mars at the same time when
the worlds were forming into rocky bodies from the dust and gas of the
original Sol system?

I wonder how many other moons Mars may have had which did not
survive to the present day?