Depends on a lot , are you planning on getting clients? While the quality of iPhones has gone up a lot in the camera- it would look weird showing up to set with an iPhone to shoot with if they’re paying you. A real camera gives you the right visual look for the project but makes you look more like the right person for the job when you show up.

Get the BlackMagic app for your phone. I’m pretty sure that it shoots in 4K and the quality is to die for. The files are big though, but because of that you can zoom in to 200% in your edit suite with no loss of detail. In fact I have found that the digital zoom on the phone isn’t all that (and I have a 14).

On the filming side of things, shoot plenty of wide/medium shots, THEN shoot close up. I edit professionally, and have lost count of the number of times I am presented with rolls of close ups, with no wides or ‘establishers’. It’s incredibly frustrating… Close ups are great, but you have to get a sense of where you are, what the person is doing, before you get into the sexy close up stuff.

If your partner is doing an action, try to get her to do it twice, wide and in close up, it makes it much easier to cut together.

That should get you started. There’s loads more but, because I don’t really know what you want to finish up with, I’m not really sure what else to add.

Oh, one more thing. Don’t shoot any single shot less than 30 seconds and, depending on the action, maybe longer. It sounds indulgent but it really isn’t - don’t shoot yourself short, lol!

Have fun!

EDIT: Whilst BlackMagic is great, it doesn’t automatically finish up in the ‘photos’ folder on your phone. You will need to transfer them out; I use the WeTransfer app to transfer them - you then send an email link to yourself and download them directly onto your laptop.