What does the sound Fang Feiqie mean in the seal script of Shuowen Jiezi?

To pronounce two words together

It means to pronounce the initial consonant of the first word and the final rhyme of the second word together.

As shown in the picture below, "luxury" is pronounced as "she" by combining the initial consonant "sh" of the style and the final "e" of the rhyme "che".

Fang Feiqie, that is, "fei"