Although gold has an international value and is therefore not less expensive in Phuket than elsewhere, the peculiarity of gold used by Thai jewelers can make it attractive for people vacationing on the island. Indeed, the gold used in the manufacture of jewelry is much purer than in the West. In Thailand, the gold standard is 23K, when it is only 18K in most Western countries. That is the reason why Thai gold has a different color than the gold you are used to see.
Thais women and also men are big fans of gold, and jewelry they possess are used as banks and it is not uncommon for them to invest in gold for resale and get fast cash during lean times.
There are many jewelers selling gold in Phuket, but the most interesting for you is probably to go to the old part of Phuket Town and more specifically to Ranong Road, where dozens of shops sell gold.