Conversation:

Looking for some help regarding phenotypes. If two people who have brown eyes have the same phenotype for eye color, which is true:

they must also have the same genotype for eye color,
their genotypes must be different,
they may or may not have the same genotype, or
it is impossible to determine without more infor

Answer:

They may or may not have the same genotype.

Their phenotype is brown eyes.
Their genotype might be either BB or Bb.
(If you are familiar with Mendelian genetics).

In short, they could have a purely brown eyed genotype (BB), OR either or both of them could also carry the recessive blue eyed gene (b) as well as the dominant brown eyed gene (B).

The only way to find out would to be to perform controlled crossing experiments, and this is frowned upon when done with humans.