What term describes Greek-based morphemes such as -phon- and -bio-?

The term that describes Greek-based morphemes such as -phon- (related to sound) and -bio- (related to life) is known as a combining form. Combining forms are used in the formation of compound words, where they retain their specific meaning but can be attached to different prefixes or suffixes to create new words.

In this case, the combining forms can be combined with additional morphemes (like prefixes or suffixes) to form terms such as "telephone" (from -phon-) and "biology" (from -bio-). This is important in understanding how different elements of words work together to convey meaning in English and other languages that utilize Greek and Latin roots.

Other options such as root word, affix, and base word don’t precisely capture the relationship of these morphemes when they stand alone without combining with others, as combining forms specifically refer to these morphemes that are used in combination with other elements.