why can't a change in the phenotype cause a change in the genotype?

Answer 1

A change in the physical characteristics (phenotype) of a person does not depend on genetic makeup (genotype.) Plastic surgery, amputation, third-degree burns, etc, all change the physical makeup of a person, but do noting to the genetic makeup of a person.

Now, a change in the genotype of a person would definitely affect the phenotype...but I am sure you knew that already. :-)

Answer 2

if you have gene that makes you have 6 fingers, and then they surgically remove the sixth finger, do you think your genes will change too?