PHNOM PENH—In its home country, the Cambodian riel has long played second fiddle to the U.S. dollar—but a new stock exchange and government de-dollarization policies could bolster it in coming years, policy makers and experts say.

Dollars change hands with greater frequency than riel in the capital city, though both are universally accepted. Some taxi drivers say they prefer the U.S. currency simply because it means handling fewer bills; there are 4,000 riel to the dollar.

A...