Is DEET (as in the mosquito repellent), a substituted phenethylamine?
While I feel like this might be a better question for the chemistry SE, lets take a look at the molecular structures:

The basic structure of a phenethylamine (left, modified from here) versus DEET (right, modified from here):



The important chemical differences are:


DEET only has a C-alpha between the nitrogen and the ring, whereas phenethylamines have a C-alpha and a C-beta (see red annotation)
DEET has a carboxylic functional group (an amide bond), whereas phenethylamines have an amino group (see green boxes)


Taken together these differences mean that DEET is not a phenethylamine.