Phytochrome is a protein - check out the details at https://en.wikipedia.org/wiki/Phytochrome. I doubt whether it will be possible to synthesize in the laboratory unless you have lots of time, money and a protein synthesizer. You can extract the protein from plants - look at this reference https://www.acs.org/content/acs/en/education/whatischemistry/landmarks/isolation-of-phytochrome.html