As Jimi Oke details out, it won't make any difference what letter the phrase commences with, but what sound it starts off with. Considering the fact that "regular" starts off with a 'y' audio, it should really get 'a' in lieu of 'an'. SpacecatSpacecat 1311 gold badge11 silver badge33 bronze https://petskyonline.com/blog/why-tofu-cat-litter-is-gaining-popularity-in-the-uae/