The phrase "one of the Reptilia" is commonly used to refer to any species or group of reptiles. However, there are many synonyms for this phrase that can add variety and specificity to writing or speech. Some alternative phrases that can be used include "a member of the reptilian family," "a reptilian species," "a reptilian creature," or simply "a reptile." Other more specific phrases might include "a chelonian," which refers specifically to turtles and tortoises, or "a squamate," which refers to lizards and snakes. Ultimately, the best synonym will depend on the context of the situation and the desired level of specificity.