Flat photos are the usual beginner result, and the cause is rarely the camera or the phone. Something about how the light reaches the subject is doing it.
Your first day
Starting takes twenty photos of one small object near a window with soft daylight, no flash. Nothing needs to be bought first, whatever camera or phone you already own is enough. Photograph it from directly above, from eye level, from below, and from close and far, moving yourself or the object but never touching the lights or curtains. Afterward, put your best and worst shots side by side and look at where the shadows fall.
Shooting with your back to the light source out of habit is the thing to avoid. It flattens everything and kills shadow detail. Turning the object, or yourself, so the light comes from the side produces far more depth than most beginners expect.
The thing most people miss
Take two photos of the same plant, on the same phone in the same minute. Take the first with the lamp behind you, then turn the plant forty-five degrees so the window light hits the leaves from the side and take the second. The second has real shadow between the leaves. The first looks like a sticker.
Once you stop thinking about gear and start walking around a subject to find the light before raising the camera, photos stop looking flat.
How you'll know it's working
Your best shots will share one thing: the light came from the side. When you can see shadow between leaves or a soft edge running along the object, the light is working. Flat shots will have no visible shadow anywhere.
A shadow is what actually gives an object weight in a photo, not the object itself. Composition rules like the rule of thirds are worth learning once there's real depth already in the frame to arrange, not before.