My aunt has bought me an iphoneX at my birthday.
My aunt bought an iPhone for me on my birthday.
我姑妈在我生日那天给我买了一个iPhoneX手机的意思就是我姑妈在我生日当天买了一个iPhoneX手机并把手机当作生日礼物送给了我。这两句之间是递进关系可以写成并列句。
