There are several synonyms for the phrase "know only by name," which means that you have heard of someone or something, but do not have any personal experience with them. One synonym is "unfamiliar," which implies that you have not had contact with someone or something before. Another option is "unknown," which suggests that you have heard of someone or something but have never encountered them in person. "Obscure" is also a good synonym, suggesting that the person or thing is not well-known or widely recognized. Finally, "anonymous" might fit the bill, particularly if you have heard of someone without knowing anything specific about them.