1. My older (or elder) brother is working for his Ph.D.
2. My older (or elder) brother is working for his doctorate.
以上是两种简单而道地的英语.
My brother 可为兄或弟,所以吾兄一定要用My older or elder brother来 表示.
Ph. D. 后面不要再加 degree.
Note: 本人已在海外生活了数十载.为了慎重起见,我的答案都与老美或老英交换过意见,你放心使用吧.