This is the set of observable characteristics of an organism, includes it’s physical properties, how it develops, it’s behaviors. Essentially, this is the set of markers that make Thing A different from Thing B.
This things may be caused on genetic makeup (the “genotype”), or they may be caused by the environment in which the organism has developed.
For a human, these characteristics might be height, eye color, limb length, natural body fat percentage, cardiac capacity, etc.
Why I Looked It Up
In a book about the performance of Black athletes:
Preliminary research indicates that different phenotypes are at least partially encoded in the genes – conferring genotypic differences, which may result in an advantage in some sports.
The book is about racial differences, so it notes that there are many difference phenotypes across races, but also within races. Two random White people might have more divergent phenotypes than a particular White person and Black person.