I have Minecraft Java Edition on my windows computer. Is there any way to link those worlds to my iPhone 12? I want to be able to access the worlds from my phone, as well as my computer.
You can't. Minecraft Bedrock and Minecraft Java are two different versions. You can't directly link them together to edit the same file at the same time. However, there is another way.
You can convert the file to bedrock and add it to your phone. There is a tool called Je2be and there are a few tutorials on it. One tutorial:
After converting the file, you can transfer the file to your phone.