I also had an Android phone from 7th grade to 12th grade, and definitely faced the same attitude/behaviour your son experienced.
First, you should address the bullying. That is the most important part, kids are vicious and the phone might just be an easy excuse to pick on your son. You should raise this issue with other kids' parents as nicoburns said.
Second, it can definitely be a bit isolating being the only one or the few kids with an Android phone (especially in the States) a lot of social activity revolves around the Apple Ecosystem (iMessage, iMessage Games, FaceTime, etc...). I found that when I got an iPhone I felt a lot more "connected" to my peers simply because we shared the same platform, its unfortunate but it is the reality.
Third, and this may be controversial, I would get your son an iPhone, I assume the dependence for cell phones has only gotten increasingly higher post-covid and feeling left out at that age can hurt pretty bad. You could perhaps make him "earn" it by doing chores, getting good grades, etc...