No, phenylalanine is an essential amino acid which is used to make proteins in the body. Aspartame aside, it is found in protein food sources, e.g. meat, fish, eggs, dairy, nuts and legumes. If excess amino acids are consumed (i.e. more than is needed for producing proteins) they are deaminated by the liver. The amine group is metabolised to urea and excreted in urine, while the rest of the molecule is oxidised to produce energy.
However, in aspartame, the phenylalanine and aspartic acid molecules are joined together by a methyl ester which forms a small amount of methanol when aspartame is broken down. The methanol is converted to formaldehyde and then to formic acid, which is excreted in urine. Methanol found in food sources such as fruit, vegetables and alcoholic drinks is metabolised in the same way.
https://en.wikipedia.org/wiki/Aspartame