The first photo is without photoshop. Pure Green Screen. The second is a rough attempt at adding shadows.
Both of these images look photoshopped. How can I make them look realistic?
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Take a better photograph to begin with. When editing photographs, there's an age-old adage that applies: You can't make a silk purse from a sow's ear.
The photograph of the phone, hand and table is very poor quality. It looks like you used a phone camera to take it. It's blurry, noisy, out of focus, the lighting is poor, and the white balance isn't right. Then it looks like you inserted a much better quality photograph into the phone photograph. That's what makes it look out of place.
If you can't take good photos yourself, then buy a stock photo, or hire a photographer, or find a friend with a real camera and some skill in photography and lighting.
Your new version with grey backround is not much better. It is like a grey plane with a framed hole in front of green plants, there's no separate phone body.
This can be more like the wanted one:
Perspective version. The body of the phone is still only a drawing (=a rounded extruded rectangle, elementary non-photorealistic rendering).
The far end of the glass reflects more due the more gentle angle. That's simulated with layer mask.