Look at the CS degree as more than a piece of paper. Right now, you're doing PHP web development. That's the low-end of the programming totem pole and unlikely to open any doors in the future. Advancement is possible, but would be a whole lot easier with a degree. Not just because of the piece of paper, but because of what you'll know.
You've taught yourself programming, and you've been doing it in the real world. That shows you've got the drive and ability to learn more. So look at the degree as a chance to fill in a whole lot of gaps. I wish the team I'm on now had more people who actually remembered anything they learned in college.
You'll be able to learn more about algorithms and when to use what. Sure, they're almost all in libraries these days, but you have to know when to use what. Use your classes as a chance to learn more about larger systems and architecture styles. Most schools now have group-based labs where you can get a bit of practice as a group lead.
If you want to, you can gain a lot more than a piece of paper. You'll be more flexible when your current job gets shipped to India and you'll be able to find better ways to help your clients or company.