Phenylalanine is an essential amino acid (a building block for proteins in the body), meaning the body needs it for health but cannot make it.
taken from: Phenylalanine
Tyrosine is a nonessential amino acid the body makes from another amino acid called phenylalanine. It is a building block for several important brain chemicals called neurotransmitters, including epinephrine, norepinephrine, and dopamine. Neurotransmitters help nerve cells communicate and influence mood
taken from: http://www.umm.edu/altmed/articles/tyrosine-000329.htm
and i found this: