I'm gonna have an interview that will include talking about php. Problem is, I haven't touched php in 5 years. What do I need to know to sound like I know what I'm talking about? "Mmm yes I really like Laravel dependency injection, it makes managing dependencies so much easier"?

If you talk about Laravel, throw some package names at them, they'll know that you know some things like

Sanctum, Passport (API), Composer, Spatie, Barryvdh/Dompdf, IoC container, Octane, Swoole etc.

How much of the job is PHP?

PHP hasn't been my main focus for a few years, but I have used this, this, and this. What I have focused on lately is this, this, and this.

I suggest you read up on PHP 8.0 to the upcoming 8.3

If you would try that with me you won't get hired. I would read right through the bullshit trying to hide the gaps.

Of course it depends on the person interviewing you but I would focus on ensuring they have a good idea of who you are as a person and the knowledge and experience you do bring. Assuming you were a good (PHP 7) dev that should be plenty.