I read very conflicting answers here. I am from Singapore. Fully vaxxed 3 doses with a medical cert from bkk for recovered patient. (Got jackpot arriving in bkk on 15th Feb). Doctor in bkk told me no need pre pcr. Just show medical cert going to Cambodia after 7 days. 14 days later, was turn away from bkk airport, for not having pre pcr. Said Cambodia dont give <deleted> about covid recovered patients. Had to take an express pcr for 4,700baht to catch an evening flight on the same day.
Upon arrival in Phnom Penh, take an antigen test. Before taking, I showed the medical cert to medic officer. No deal..Take your antigen here. Thats my personal experience 2-3 weeks ago.
In summary, pre pcr required from bkk to pp. Thaipass and pre pcr back from pp to bkk.