For domestic airplane travel can I just get on the plane normally without any extra red tape or document/certificate requirements?

Contact the airline. They will know.

It may vary by destination. There are special requirements for Phuket, for example

When they first announced domestic flights were available there was no special requirements for a flight to Bangkok. 

If flying to other provinces it depends upon the one you are traveling to.

15 minutes ago, ubonjoe said:

When they first announced domestic flight were available there was no special requirement a for a flight to Bangkok. 

If flying to other provinces it depends upon the one you are traveling to.

Thanks, I haven't been able to get the airline support number (Thai Smile) to answer the phone (tried website, app, booking email numbers). They're obviously understaffed because of Covid economic impact. I think it's likely there won't be any requirements and I can just board since I'm going to Bangkok. Appreciate your reply.

This was from a week ago, so it could be out of date

So actually, when leaving the Phuket Sandbox to Bangkok (or anywhere else I'd assume) it's required to display to the airline a certificate from the hotel that affirms having completed the required 14 nights of quarantine in Phuket. The hotel actually forgot to give it to me when I checked out and then called me after I'd been on the road for ten minutes, so the driver had to backtrack to the hotel so I could receive that certificate.

11 hours ago, wml22 said:

So actually, when leaving the Phuket Sandbox to Bangkok (or anywhere else I'd assume) it's required to display to the airline a certificate from the hotel that affirms having completed the required 14 nights of quarantine in Phuket.

Not according to the info posted above. Nothing is needed to fly to Bangkok. But from there to other provinces it is needed.

If traveling overland you would need your covid test certificate and/or proof of being vaccinated to enter other provinces.

9 hours ago, ubonjoe said:

Not according to the info posted above. Nothing is needed to fly to Bangkok. But from there to other provinces it is needed.

If traveling overland you would need your covid test certificate and/or proof of being vaccinated to enter other provinces.

As far as I could tell, the airline would not have permitted me to leave Phuket without showing the Sandbox completion certificate. So I wanted to update that info into this thread in case anyone else is in a similar situation. Interesting that it's not apparently a general requirement. Maybe because I'm on a visa exempt entry, I was subjected to that requirement. If I'd already changed to a longer term visa then it wouldn't have been required I'd think.