Do you need a PhD to work on AI Safety?

No, but it helps. Some great resources if you're considering it, are: https://rohinshah.com/faq-career-advice-for-ai-alignment-researchers/ https://80000hours.org/articles/ai-safety-syllabus/ https://80000hours.org/career-reviews/machine-learning-phd/

The first two links show general ways to get into AI safety, and the last will show you the upsides and downsides of choosing to make a PhD.