"Subj + 打電話 + Obj" vs "Subj + 給 + Obj + 打電話"
我 晚上 要 打电话 媽媽 : This is invalid.

In the phrase "打电话", "打" is the verb and "电话" is the object. And the "打" here is not a verb that can take two objects. So you must use: 我 晚上 要 給 媽媽 打電話