Fmoc-4-(phosphonomethyl)-Phe-OH is primarily used in peptide synthesis, particularly in solid-phase peptide synthesis (SPPS). It serves as a protected amino acid derivative, enabling the incorporation of phosphonomethyl groups into peptide chains. This modification is crucial for studying phosphorylation processes and mimicking phosphorylated amino acids, which play significant roles in signal transduction and protein regulation. The compound is also valuable in developing peptide-based inhibitors and probes for biological research, aiding in understanding enzyme mechanisms and interactions. Its application extends to drug discovery, where it helps design peptides with enhanced stability and bioactivity, particularly in targeting phosphoprotein-related pathways.