Also, ester formation usually takes hours rather than minutes. Use conventional heating under reflux, and model your ester synthesis after the mandelic acid ester syntheses in this document: https://www.thevespiary.org/rhodium/Rhodium/chemistry/pemoline.html (https://www.thevespiary.org/rhodium/Rhodium/chemistry/pemoline.html)
The isopropanol ester of phenylalanine has a boiling point of 128-131°C/5 mmHg, and is not crystalline, but it may form a solid hydrochloride salt if you gas an anhydrous toluene solution of the washed and purified ester using anhydrous HCl gas.