I have a D3200. I also have a brand new Galaxy S21 Ultra that has a 108mp camera and 5 other cameras for all sorts of fun effects.
I would shoot with the 3200. Take some with the cell phone, but here's the difference. DSLRs manipulate mechanical things inside the camera and open a shutter/aperture to allow photons of light to hit a sensor. Cell phones use software to compile data and combine it into what the AI THINKS you were shooting and sometimes the results are hideously dirty and awful. Search for "panorama fails" for just one example of what I'm talking about.
This photo below was taken with my S21 Ultra. It lit up the screen to give some ambient light on my face, and the background is a campfire. Take note that this is at midnight on NYE, I'm on the top of a mountain in the dark, and the only light was from the fire and my screen.
Aside from how damn sexy I am, notice a few things. The way the camera took this photo was to open the shutter for about 6 seconds and (despite having no way of preventing shake) it recorded what light was hitting the sensor, where those same colors and values were moving, trying to track them, then once it absorbed enough light, it attempted to reconstruct my features using software. My whiskers are completely non-coherent, my eyes are uneven, and it placed random jet-black whiskers around my chin. Overall, you can look at it and say "that's Curtis!" but as a quality picture, it isn't. It's a bunch of noise that some software put together that looks kind of like Curtis.
A DSLR manipulates mechanical settings in the camera body and lens. It opens the shutter and absorbs whatever it absorbs in the time and area you give it. Take a look at even the smallest lens for that D3200. It houses a dozen fine-crystal lens elements flawlessly aligned in a precision housing. Your cell phone has a 15mm glass disk. I don't care how many zillion pixels a camera has, if it doesn't have the optics to feed it quality photons, it will suck. Kinda like those little "1080p spy cameras" that are the size of your thumbnail. There might be 1080 lines on the sensor, but that 1/2 mm pinhole lens is going to make the resulting video look like a VHS tape you found in your attic from 1983.
For your shots on the D3200, you can go full auto. Just put in on "Auto" (or some have a green icon) and shoot. You also might find that Shutter Priority (usually "S" on Nikons) might be helpful if you're having trouble with light. Try to keep the shutter speed faster than 1/20 for normal focal ranges and even faster the more you zoom in. If you have plenty of light, you might find Aperture Priority a nice thing. You can scroll to higher numbers (smaller apertures) to get deep focal depth in case you want to include more of the fore/background, but weddings tend to be all about the couple. Scroll that wheel down to get F3.5 and the guests and flowers in the foreground and background just turn into fuzz.
Above all, give yourself some grace. I'm was a photography minor in college and even I don't do weddings. I do landscapes. Mountains and trees don't move so you can take your time and play around. You won't be a master, but you'll do fine. Take the camera this week and READ THE MANUAL. There are some "rules" that the camera makes. For instance, on Auto there isn't much you can change. It takes control. Program mode is kind of nice because it does the metering part, but you can use the wheel to change that proper exposure it selects. For instance if you meter on a race car and it says F5.6 and 1/500, you can take the photo but you'll have a car that looks like it's parked because the fast shutter will freeze things. Instead you can scroll the wheel to go for a smaller aperture and a longer exposure so the wheels are blurred. Bingo. Action shot. Same amount of light getting through, but it lets you manipulate how it gets there. Above all, you need to know which modes allow multiple shots. Some modes are single shot only. That gets frustrating at a wedding.
Also, it's digital. Stuff a big card in there and you can take thousands of shots. When they're putting rings on each other's fingers, take 20 exposures, click the wheel one way or another a couple clicks, take 20 more. A few more clicks of the wheel, take 20 more.
Settings; I suggest you record photos in RAW+jpg. Most formats like tiff, jpg, or other common image files are the end result. They are a picture. There is a red pixel at this coordinate and a blue one at this coordinate. A RAW image file contains all the metadata for every single pixel. A jpg file is like a poster of a Van Gogh printed on paper. A RAW file is Van Gogh's original painting. We can see the brush strokes, chemically analyze the paint, use carbon dating, hey look we found DNA from his ear, yadda yadda. If they end up being edited by a pro, having all that data separated out is super nice for editing. You remember the scene from the Matrix where Joey Pants is looking at the green characters on a screen and he says "You get used to it. All I see is blonde, redhead." RAW file is the green code on the screen. "blonde/redhead" is the jpg. When you select RAW+jpg, it will record each frame as both a jpg for quick viewing and a RAW file for editing.
In all honesty, the manual (find one on Nikon's page I assume) has all of this stuff in it. It's pretty clear. You need to read the section on settings anyway. And play with it. Take all the photos. See what works and what doesn't. You'll find that spending time with it is like driving a new car. It takes you a bit to intuitively know where the headlight switch is or the limits of understeer, but once you get used to it you'll be changing shutter speeds and apertures in no time.
