The phrase "enter up on" is not commonly used in English language, and therefore, there are no specific antonyms for it. However, we could consider antonyms for the individual words "enter" and "up on." Some antonyms for "enter" could be leave, exit, or depart. On the other hand, some antonyms for "up on" (meaning knowledgeable or informed about something) could be unfamiliar or ignorant. It is essential to use words correctly and accurately to communicate effectively with others. Using the right antonyms can help you express yourself clearly, and ensure that your message is understood correctly.