yes you need a RT-PCR test check with your airline because my airline say I have to have a 48 hour test even though Thailand say you need a 72 hour test and you do not need it for your Thai pass just show once you arrive in Thailand…
If he is landing on 31st he will have to do sandbox and then you will have to apply for his Thai pass and if so he must have a direct flight to Phuket he can not get a domestic flight from Bangkok it must be a sealed vtl flight ✈️