The Phuket program has been changed to 14 days even if vaccinated. But you can go around the island and not be stuck in your room. The plan should be finalized by end of next week and starts July 1. But could be cancelled still
The current plan best case scenario is July 1 for Phuket and oct 1 for Bangkok, no quarantine if vaccinated. Neither is finalized yet, and cases are making all time highs by the day so no promises.
The thai government is supposedly organizing a number of new direct charter flights starting in july 1st. She may be able to go via singapore by then, so I would have a look at that in a couple weeks. Best of luck!
Consider waiting until after July 1, Phuket should have quarantine free options by then. For quarantine, you both need to be on the same flight, no exceptions. A lot of hotels won’t even except you if you’re not married yet. But some will