Answer: Phenylalanine has no polar group in the side chain
Explanation:
Unlike phenylanine with a nonpolar methyl benzyl group in its side chain, tryptothan and tyrosine on the other hand possesses a polar indole ring and hydroxyl group in their side chain respectively, which helps them form hydrogen bonds with water molecules.
Thus, both are less hydrophobic (water-hating) than phenylanine.