Can I convert my .heic photos (from my phone) to RAW files? In PS? In LR?

A rendered file can't be turned into a raw camera file. 

This is similar to expecting to be able to extract raw eggs or flour from a baked cake.

It is possible to save a rendered file into a DNG file, but that doesn't convert it into a raw camera file.

If you want raw camera data from an iPhone, then you need to install and use a 3rd party app that supports raw data, or if you have a "Pro" model phone there are other options.