Citigroup is merging its voice and electronic trading businesses for currencies, marking the latest in a series of changes at the senior levels of the bank's foreign-exchange ranks.

In a memo reviewed by The Wall Street Journal, Jeff Feig, global head of foreign exchange at the bank, said Richard Bibbey will become the head of global spot FX trading, encompassing trading over the phone and over electronic systems. The bank didn't have a combined global head of spot trading previously.