I'm not sure about the 5 or 7 day rule, I believe it's still 7 days as I haven't heard of 5 days for Phuket.
On the other hand Royal Vacations (which I'm planning to use around the same time) does also include the required insurance, PCR tests and a one way airport transfer in the price so it would work out cheaper than doing it all separately plus they do the leg work and while it's easy to do, why not chose them if it's cheaper at the same time.
If you check out a YouTuber called chocolate man in Thailand he used them about a month ago so check out his previous vids.