Disable Apple Photos from launching

For Yer_Man's Option 2: Click on a RAW file, and key command-i to bring up the info window for the file

Click on "Open with" to get a list of apps that you can choose to be the one that will open files like this one. Then choose "Change all..."

Easiest option: don't double click on a Raw file. If you have LRC there's no need to use ACR at all, it's already built in to LRC. So import your raws to LRC and work from there.

Option 2: Set another app as the default app for these raws - assuming you don't go for option 1. Which app do you want to use?

With the iPhone connected to your Mac with its charging cable launch Image Capture. Select "No Application" in this menu:

So connecting my iPhone and changing those settings, will in turn change the settings for when I double click to open a CR3 file in finder?

No. For that pick the app you want to open for your CR3 files and do as Richard Taylor says, above. And I do love a bit of snark, but if you use the apps they way they are designed to be used you simply won't have this issue at all...

Yeah I am aware LRC and ACR are very similar

No they're not similar. They're the same. ACR is rolled into LRC. I get you like your workflow but you're making life unnecessarily complex for yourself. But however...