I would like to make a template using this image and make multiple outputs with different textured images as a clipping mask. I tried recreating it using inner shadows but was not successful (I'm a beginner).
Is there a way to use clipping masks without losing these shadows?
I am not entirely sure if I have understood your question correctly, but I'll take a guess that you are trying to insert some design/pattern into the phone cases, while retaining the shading.
The image you posted already has a transparent background.
If you look at the example below, I have clipped the "Floral pattern" layer to the "Phone" layer. Then I changed the layer blending mode of the Floral pattern layer to Multiply, so that the shading shows through from the layer below.
You can put your phone to the layer mask of an image layer. That image can be your phone or something else.
Your image has indexed colors. Convert it to RGB mode to be able to use the grayshades.
You can copy the phone to its own layer mask by copying it at first to the clipboard. Then create a layer mask to the pone layer. Alt+Click the layer mask icon in the layers panel. That brings the mask onscreen. Paste in place the clipboard content to the mask. Click the image icon in the layers panel to see the image.
Invert the layer mask. All white has turned to black and those areas in the image are now transparent. Only click the mask icon before editing it. The affected image stays visible.
Apply the curves tool to the layer mask if you want to adjust the steepness at grey areas.
Here's a test. The curves is just applied to the layer mask. Decreasing slope inverts the mask at the same time. A colored test background has been inserted to show the tansparency:
Applying the image to itself as layer mask probably isn't the wanted effect. In the next test version the image layer is solid black and the mask is again under adjustment with curves:
You can fix the effect by Applying the layer mask. I see this not useful in Photoshop because generally one wants to retain max editability.
ADD: User Billy Kerr seemingly has shown a short way to use your image to shade a texture. Use it and do not mess with masks, if you want the shading effect.
