Talk to your professor
As the other answers have said, professional help is important for your overall quality of life. But it's also a long term solution, and you also have to deal with your labs this semester. Talk to your professor about how you can be successful in your current labs while you seek professional help.
Be prepared for your professor to be dismissive of your concerns
While there are many wonderful and empathetic professors out there, not all of them are such, and there's no guarantee that you have one of the good ones. An unfortunately large percentage of the population is dismissive of any emotional stresses that they do not personally feel. As an experienced biologist or chemist, your professor is probably very comfortable with dealing with hazardous chemicals, and may not remember that not everyone feels the same way. On the other hand, they're also a teacher who has likely dealt with all manner of students in the past, and may very well have helped other students with similar phobias to yours in the past.
Hope for the best, but prepare for the worst.
Focus on your reactions to your fear, not the fear itself
The truth of the matter is that many of the chemicals used in labs are hazardous when mishandled. A healthy respect for chemicals is something that most professors are going to want to encourage, not discourage. The problem lies not with your fears, but in how your phobia causes you to react - shaking, holding your breath, making mistakes, etc.
Frame this as a safety issue (which it is) - your phobia makes it unsafe for you to handle chemicals. This moves the discussion away from "how are you mastering your phobia" and "is your fear rational" (which are issues for you and your professional help) and into the realm of "How will you participate in labs safely while you are mastering your phobia." Don't let your professor side track you into a discussion of the whys and hows of your phobia. Focus on the practical effects that your phobia causes, and how those make it dangerous for you to work in the lab.
Also, lab safety is a serious concern, and gives you grounds to escalate the issue if your professor tries to dismiss your concerns. (Not that you wouldn't have grounds anyways, but lab safety gets a lot more respect than mental health, and your escalation is more likely to be taken seriously)
Consider solutions ahead of time
Before you talk to your professor, brainstorm for ways that you might be able to make the class manageable. Maybe you get a lab partner (or two, if the labs are designed for two bodies) who can managed the chemicals while you make observations from a safer distance. Maybe you act as an observer to all the students doing labs, and don't participate yourself. Try and come up with as many possible solutions as you can, and consider how effective you think each one would be, and why.
This will help prepare you to discuss these solutions with your professor, and find one that's workable.
If you do manage to find professional help before the beginning of classes, talk to them about how to best approach your professor - they'll probably have better advice for you than some random person on the internet.
On the flip side, your school probably has some resources to help you find the professional help you need. Your chemistry and bio departments may even have experience with very similar phobias to what you currently face.