This is not the usual spelling in any of the Scandinavian languages (in Sweden and Denmark it is Freja and in Norway it is Frøja) but it is the common spelling of the goddess's name in English. In the 2000s it became popular in Britain.
Due to the renown of the saints by this name, Gregory (in various spellings) has remained common in the Christian world through the Middle Ages and to the present day. It has been used in England since the 12th century. A famous bearer from the modern era was American actor Gregory Peck (1916-2003).
The Cornish form of this name, Jennifer, has become popular in the English-speaking world.
As an English name, it became popular due to the Fleetwood Mac song Rhiannon (1976), especially in the United Kingdom and Australia.