The antonyms for the phrase "checked up" include neglected, ignored, dismissed, avoided, and overlooked. Neglected refers to the failure to give attention or care to something. Ignored connotes intentionally disregarding something. Dismissed means to reject or set aside something. Avoided implies staying away from something intentionally. Overlooked means to miss or fail to notice something. It is essential to note that these antonyms have a negative tone, and it is always best to check up on things or people regularly to avoid any potential problems that may arise from neglect or disregard.