Can I find online English teaching work in Siem Reap?

With limited experience and no TEFL certification, your choices are somewhat restricted. You might consider obtaining a basic TEFL certification, which can be done inexpensively. This would then allow you to apply to platforms like Preply and Amazing Talker. Many people teach online in Cambodia, and all you need is a reliable internet connection and a laptop. You can focus on conversation skills, avoiding grammar and other topics you're not comfortable with.