"不是小是大" (bú shì xiǎo shì dà) in Chinese means "not small, but large."
In Engpsh, we can say "not small, but big" or "neither small nor small, but big."
Here are some example sentences:
"The elephant is not small, but big." (Chinese: "大象不是小的，而是大的。" dàxiàng bú shì xiǎo de, ér shì dà de.)
"The car is not small, but big." (Chinese: "这辆车不是小的，而是大的。" zhè pàng chē bú shì xiǎo de, ér shì dà de.)
"The house is neither small nor small, but big." (Chinese: "这所房子既不是小的，也不是小的，而是大的。" zhè suǒ fángzi jì bú shì xiǎo de, yě bú shì xiǎo de, ér shì dà de.)