Phka Kn'jay is a little boutique run by a charming and very friendly tailor named Pich Thavey. The shop has a variety of women's clothing, all beautifully tailored and most in linens and cottons.
Pich will also make custom clothing. I bought in a skirt and top and he made perfect copies. I had a lot of fun deciding on designs and fabrics to use.
It probably works best if you bring in clothes you want copied or a photo of what you want. The store has some fabric to choose from, but you can also bring your own.
For some reason I can't type in the address of the store, but it's a few stores away from where it is on the map. It's at 14A, Street 242.